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This article explores the movement of sarcomeres in the heart muscle and the role of the protein titin in this process. It challenges previous beliefs by showing that sarcomeres do not all move in synchrony during muscle contraction. The asynchrony is influenced by factors such as sarcomere length and calcium levels. The article suggests that this asynchrony may contribute to impaired heart function in conditions like dilated cardiomyopathy. Further research is needed to understand the link between sarcomere movement and heart disease. [Extracted from the article]

Skeletal muscle tissue increases or decreases its volume by synthesizing or degrading myofibrillar proteins. The ubiquitin–proteasome system plays a pivotal role during muscle atrophy, where muscle ring finger proteins (Murf) function as E3 ubiquitin ligases responsible for identifying and targeting substrates for degradation. Our previous study demonstrated that overexpression of Ozz, an E3 specific to embryonic myosin heavy chain (Myh3), precisely reduced the Myh3 replacement rate in the thick filaments of myotubes (E. Ichimura et al., Physiol Rep. 9:e15003, 2021). These findings strongly suggest that E3 plays a critical role in regulating myosin replacement. Here, we hypothesized that the Murf isoforms, which recognize Myhs as substrates, reduced the myosin replacement rates through the enhanced Myh degradation by Murfs. First, fluorescence recovery after a photobleaching experiment was conducted to assess whether Murf isoforms affected the GFP-Myh3 replacement. In contrast to Murf2 or Murf3 overexpression, Murf1 overexpression selectively facilitated the GFP-Myh3 myosin replacement. Next, to examine the effects of Murf1 overexpression on the replacement of myosin isoforms, Cherry-Murf1 was coexpressed with GFP-Myh1, GFP-Myh4, or GFP-Myh7 in myotubes. Intriguingly, Murf1 overexpression enhanced the myosin replacement of GFP-Myh4 but did not affect those of GFP-Myh1 or GFP-Myh7. Surprisingly, overexpression of Murf1 did not enhance the ubiquitination of proteins. These results indicate that Murf1 selectively regulated myosin replacement in a Myh isoform–dependent fashion, independent of enhanced ubiquitination. This suggests that Murf1 may have a role beyond functioning as a ubiquitin ligase E3 in thick filament myosin replacement. [ABSTRACT FROM AUTHOR]

The molecular motor myosin is post‐translationally modified in its globular head, its S2 hinge, and its thick filament domain during human skeletal muscle aging. To determine the importance of such modifications, we performed an integrative analysis of transgenic Drosophila melanogaster expressing myosin containing post‐translational modification mimic mutations. We determined effects on muscle function, myofibril structure, and myosin biochemistry. Modifications in the homozygous state decreased jump muscle function by a third at 3 weeks of age and reduced indirect flight muscle function to negligible levels in young flies, with severe effects on flight muscle myofibril assembly and/or maintenance. Expression of mimic mutations in the heterozygous state or in a wild‐type background yielded significant, but less severe, age‐dependent effects upon flight muscle structure and function. Modification of the residue in the globular head disabled ATPase activity and in vitro actin filament motility, whereas the S2 hinge mutation reduced actin‐activated ATPase activity by 30%. The rod modification diminished filament formation in vitro. The latter mutation also reduced proteostasis, as demonstrated by enhanced accumulation of polyubiquitinated proteins. Overall, we find that mutation of amino acids at sites that are chemically modified during human skeletal muscle aging can disrupt myosin ATPase, myosin filament formation, and/or proteostasis, providing a mechanistic basis for the observed muscle defects. We conclude that age‐specific post‐translational modifications present in human skeletal muscle are likely to act in a dominant fashion to affect muscle structure and function and may therefore be implicated in degeneration and dysfunction associated with sarcopenia. [ABSTRACT FROM AUTHOR]

Considering the occurrence of serious heart failure in a gene knockout mouse of PIP5Kγ and in congenital abnormal cases in humans in which the gene was defective as reported by others, the present study attempted to localize PIP5Kγ in the heart during prenatal stages. It was done on the basis of the supposition that phenotypes caused by gene mutation of a given molecule are owed to the functional deterioration of selective cellular sites normally expressing it at significantly higher levels in wild mice. PIP5Kγ‐immunoreactivity was the highest in the heart at E10 in contrast to almost non‐significant levels of the immunoreactivity in surrounding organs and tissues such as liver. The immunoreactivity gradually weakened in the heart with the prenatal age, and it was at non‐significant levels at newborn and postnatal stages. Six patterns in localization of distinct immunoreactivity for PIP5Kγ were recognized in cardiomyocytes: (1) its localization on the plasma membranes and subjacent cytoplasm without association with short myofibrils and (2) its localization on them as well as short myofibrils in association with them in cardiomyocytes of early differentiation at E10; (3) its spot‐like localization along long myofibrils in cardiomyocytes of advanced differentiation at E10; (4) rare occurrences of such spot‐like localization along long myofibrils in cardiomyocytes of advanced differentiation at E14; (5) its localization at Z‐bands of long myofibrils; and (6) its localization at intercellular junctions including the intercalated discs in cardiomyocytes of advanced differentiation at E10 and E14, especially dominant at the latter stage. No distinct localization of PIP5Kγ‐immunoreactivity of any patterns was seen in the heart at E18 and P1D. The present finding suggests that sites of PIP5Kγ‐appearance and probably of its high activity in cardiomyocytes are shifted from the plasma membranes through short myofibrils subjacent to the plasma membranes and long myofibrils, to Z‐bands as well as to the intercalated discs during the mid‐term gestation. It is further suggested that PIP5Kγ is involved in the differentiation of myofibrils as well as intercellular junctions including the intercalated discs at later stages of the mid‐term gestation. Failures in its involvement in the differentiation of these structural components are thus likely to cause the mid‐term gestation lethality of the mutant mice for PIP5Kγ. [ABSTRACT FROM AUTHOR]

The objective of this study is to develop and evaluate the properties of smoked edible film (EF) composed of carrageenan, myofibril, and collagen. The smoked EF was prepared by incorporating 0.8% liquid smoke. The analysis focused on various parameters including pH, physical properties such as thickness, solubility, tensile strength, elongation percentage, and water vapor transmission rate (WVTR). Sensory evaluation was also conducted to assess the texture attributes of the coated product, including wateriness, firmness, elasticity, hardness, and juiciness. The findings revealed that the concentration of the ingredients influenced the thickness of the EF, with myofibril proteins exhibiting higher concentrations compared to carrageenan and collagen. Both collagen and myofibril demonstrated maximum solubility at a concentration of 6%, while carrageenan achieved optimal solubility at concentrations ranging from 2 to 2.5%. Carrageenan exhibited significantly higher tensile strength compared to myofibril and collagen, whereas collagen demonstrated greater elasticity than carrageenan and myofibril protein. Moreover, myofibril protein film exhibited a lower water vapor transmission rate compared to carrageenan and collagen films. In terms of sensory assessment, carrageenan displayed high elasticity and juiciness, while collagen and myofibril showed high firmness and hardness. All EFs showed better antioxidant activity compared to Trolox (EC50 < 95.57 µg/mL). [ABSTRACT FROM AUTHOR]

To determine whether sarcoplasmic proteins affected water migration in myofibrils during air-drying, with protein denaturation as an indicator of sarcoplasmic protein changes, the extent of sarcoplasmic protein changes in lamb during air-drying was first studied. The results showed that sarcoplasmic protein’s thermal stability decreased and secondary structure changed, indicating sarcoplasmic protein denatured in lamb during air-drying (35 °C, 60% RH, 3 m/s wind speed). Subsequently, the effect of sarcoplasmic protein solutions, dried at different times and rates, on myofibril protein–water interaction was studied in vitro. Two sets of sarcoplasmic protein solutions were dried for 0, 3, 6, and 9 h in a drying oven, resulting in different degrees of change. These two sets with higher or lower drying rates were achieved by controlling the contact area between sarcoplasmic protein solution and air. These dried sarcoplasmic protein solutions were then mixed with extracted myofibril and incubated for 2 h. The results showed a significant increase in T21 relaxation time of the incubation system when sarcoplasmic protein solution was dried at 35 °C for 3 h. This indicated that myofibrillar protein–water interaction was weakened, facilitating water migration from the inside to the outside of myofibrils. The denaturation degree of sarcoplasmic proteins was slowed by a higher drying rate, thereby alleviating the increase in the amount of immobile water within myofibrils when dried for 6 h. In conclusion, the properties of sarcoplasmic proteins were influenced by both drying rate and time, thereby influencing the water migration within myofibrils during air-drying. [ABSTRACT FROM AUTHOR]

Bali cattle (Bos javanicus) are a local breed from Indonesia with the potential for beef production, but its meat has been reported to be tough. This indicates that there is a need to develop various methods that can be used for assessment to improve the quality of the meat. One such method is muscle scoring (MS), which is often used to predict the amount of meat in the carcass from live animals, but the muscle microstructure contributing to the quality is often neglected. Therefore, this study aims to evaluate the correlation between the muscle score of Bali cattle and the quality of muscle microstructure in terms of myofibril morphometric and connective tissue composition using a histochemistry approach. The population consisted of 31 Bali cattle, and MS was performed by evaluating the muscle line using a range of 1 to 15. The three individuals with the highest scores (Hi) and the three with the lowest (Lo) were sampled for semitendinosus muscle microstructural observation. The results showed that cattle in the Hi group had a higher surface area of myofibril and sarcomere length, but had a significantly lower relative percentage of intramuscular collagen compared to others in the Lo group (p < 0.05). Generally, muscle score had a positive correlation with body weight, surface area of myofibril and sarcomere length. In all cattle, the fibres identified were similar, where the thick types were dominant in the epimysium and perimysium, followed by the thin variants. Furthermore, the endomysium prominently contained non‐fibrous or other types of fibre. This study can provide the basic data that can be used as a pilot for future studies of muscle score assessment in Indonesian cattle. [ABSTRACT FROM AUTHOR]

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e. an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e. myofibril hypertrophy) and/or the number of myofibrils (i.e. myofibrillogenesis) is not known. Electron microscopy (EM) can provide images with the level of resolution that is needed to address this question, but the acquisition and subsequent analysis of EM images is a time- and cost-intensive process. To overcome this, we developed a novel method for visualizing myofibrils with a standard fluorescence microscope (fluorescence imaging of myofibrils with image deconvolution [FIM-ID]). Images from FIM-ID have a high degree of resolution and contrast, and these properties enabled us to develop pipelines for automated measurements of myofibril size and number. After extensively validating the automated measurements, we used both mouse and human models of increased mechanical loading to discover that the radial growth of muscle fibers is largely mediated by myofibrillogenesis. Collectively, the outcomes of this study offer insight into a fundamentally important topic in the field of muscle growth and provide future investigators with a time- and cost-effective means to study it.

The maintenance of skeletal muscle mass plays a fundamental role in health and issues associated with quality of life. Mechanical signals are one of the most potent regulators of muscle mass, with a decrease in mechanical loading leading to a decrease in muscle mass. This concept has been supported by a plethora of human- and animal-based studies over the past 100 years and has resulted in the commonly used term of 'disuse atrophy'. These same studies have also provided a great deal of insight into the structural adaptations that mediate disuse-induced atrophy. For instance, disuse results in radial atrophy of fascicles, and this is driven, at least in part, by radial atrophy of the muscle fibers. However, the ultrastructural adaptations that mediate these changes remain far from defined. Indeed, even the most basic questions, such as whether the radial atrophy of muscle fibers is driven by the radial atrophy of myofibrils and/or myofibril hypoplasia, have yet to be answered. In this review, we thoroughly summarize what is known about the macroscopic, microscopic, and ultrastructural adaptations that mediated disuse-induced atrophy and highlight some of the major gaps in knowledge that need to be filled. [ABSTRACT FROM AUTHOR]

The skeletal muscle of teleost fish is remarkable in its capacity for indeterminate growth and phenotypic plasticity to function across different environmental conditions. Generation of the sarcomeric proteins that comprise the muscle myofibrils is the single biggest contributor to protein synthesis in fish muscle. In the past decade, numerous studies have shown sarcomeric proteins, especially those of the troponin complex and myosins, exhibit altered expression in exceptionally rapidly growing fish muscle. This includes cases associated with inherent inter-individual variation in growth rates, including hybrid vigour, and induction during rapid compensatory growth. The purpose of this review is to present the evolutionary mechanisms (i.e. whole genome and gene duplication) responsible for the expanded genomic array of sarcomeric proteins found in teleost fish. On this backdrop, the parallels between then changes in sarcomeric gene expression linked with growth and those associated with thermal acclimation (an example of phenotypic plasticity) are discussed. The plasticity associated with optimizing muscle performance during thermal acclimation appears closely coupled with indeterminate growth, and I speculate on some of the endocrine factors (e.g. thyroid hormone signaling) where the two are likely to converge. Together, this review provides a timely synthesis of the determinants of sarcomeric protein expression in fish, and highlights areas ripe for future investigation. This review also emphasizes that, to facilitate comparisons between different species and across various contexts of muscle growth and plasticity, it is imperative that upcoming studies on genes encoding sarcomeric proteins in teleost fish adopt a consistent and evolutionarily-informed universal nomenclature. [ABSTRACT FROM AUTHOR]

Summary: The alkaline ionised water (AIW) could inactivate food‐borne microorganisms, ensuring the vegetables and fruits security. However, the application of AIW in preserving fish is still unknown. Therefore, the present study aimed to explore the effects of AIW on grass carp fillets during storage at 4 °C for 12 days. The results of total volatile basic nitrogen (TVB‐N), thiobarbituric acid reactive substances (TBARS), colour and the sensory attributes showed that the AIW‐treated grass carp fillets exhibited better shelf life. As for the microbial composition, AIW treatment for 5 min significantly inhibited the growth of the predominant bacteria, such as Staphylococcus and Pseudomonas. According to the result from microstructure, the neat and even structure of myofibrillar proteins (MPs) was conducive maintained the fish quality. Overall, the results demonstrated that AIW treatment exerted a protective effect of inactivating spoilage microorganisms and preserving the quality of grass carp fillets. [ABSTRACT FROM AUTHOR]

Sarcomeres are the basic contractile units within cardiac myocytes, and the collective shortening of sarcomeres aligned along myofibrils generates the force driving the heartbeat. The alignment of the individual sarcomeres is important for proper force generation, and misaligned sarcomeres are associated with diseases, including cardiomyopathies and COVID-19. The actin bundling protein, α-actinin-2, localizes to the ‘Z-Bodies” of sarcomere precursors and the ‘Z-Lines’ of sarcomeres, and has been used previously to assess sarcomere assembly and maintenance. Previous measurements of α-actinin-2 organization have been largely accomplished manually, which is time-consuming and has hampered research progress. Here, we introduce sarcApp, an image analysis tool that quantifies several components of the cardiac sarcomere and their alignment in muscle cells and tissue. We first developed sarcApp to utilize deep learning-based segmentation and real space quantification to measure α-actinin-2 structures and determine the organization of both precursors and sarcomeres/myofibrils. We then expanded sarcApp to analyze ‘M-Lines’ using the localization of myomesin and a protein that connects the Z-Lines to the M-Line (titin). sarcApp produces 33 distinct measurements per cell and 24 per myofibril that allow for precise quantification of changes in sarcomeres, myofibrils, and their precursors. We validated this system with perturbations to sarcomere assembly. We found perturbations that affected Z-Lines and M-Lines differently, suggesting that they may be regulated independently during sarcomere assembly.

The effects of reduced glutathione (GSH) on skeletal muscle fatigue were investigated. GSH was depressed by buthionine sulfoximine (BSO) (100 mg/kg body wt/day) treatment for 5 days, which decreased GSH content to ~10%. Male Wistar rats were assigned to the control (N = 18) and BSO groups (N = 17). Twelve hours after BSO treatment, the plantar flexor muscles were subjected to fatiguing stimulation (FS). Eight control and seven BSO rats were rested for 0.5 h (early stage of recovery), and the remaining were rested for 6 h (late stage of recovery). Forces were measured before FS and after rest, and physiological functions were estimated using mechanically skinned fibers. The force at 40 Hz decreased to a similar extent in both groups in the early stage of recovery and was restored in the control but not in the BSO group in the late stage of recovery. In the early stage of recovery, sarcoplasmic reticulum (SR) Ca2+ release was decreased in the control greater than in the BSO group, whereas myofibrillar Ca2+ sensitivity was increased in the control but not in the BSO group. In the late stage of recovery, SR Ca2+ release decreased and SR Ca2+ leakage increased in the BSO group but not in the control group. These results indicate that GSH depression alters the cellular mechanism of muscle fatigue in the early stage and delays force recovery in the late stage of recovery, due at least in part, to the prolonged Ca2+ leakage from the SR. [ABSTRACT FROM AUTHOR]

Myofibrils are long intracellular cables specific to muscles, composed mainly of actin and myosin filaments. The actin and myosin filaments are organized into repeated units called sarcomeres, which form the myofibrils. Muscle contraction is achieved by the simultaneous shortening of sarcomeres, which requires all sarcomeres to be the same size. Muscles have a variety of ways to ensure sarcomere homogeneity. We have previously shown that the controlled oligomerization of Zasp proteins sets the diameter of the myofibril. Here, we looked for Zasp-binding proteins at the Z-disc to identify additional proteins coordinating myofibril growth and assembly. We found that the E1 subunit of the oxoglutarate dehydrogenase complex localizes to both the Z-disc and the mitochondria, and is recruited to the Z-disc by Zasp52. The three subunits of the oxoglutarate dehydrogenase complex are required for myofibril formation. Using super-resolution microscopy, we revealed the overall organization of the complex at the Z-disc. Metabolomics identified an amino acid imbalance affecting protein synthesis as a possible cause of myofibril defects, which is supported by OGDH-dependent localization of ribosomes at the Z-disc. [ABSTRACT FROM AUTHOR]

Meat is the richest source of protein and according to meat sources, the protein is composed of different types of amino acids which are completely dependent upon the protein types. Myofibril is basically muscle protein that’s widely present in different types of fish and low quantity is present in different meat (camel). Myofibril is made up of thick and thin myofilaments chemically. Actin, tropomyosin, troponin, and tropomyosin are thin myofilaments on the other hand myosin is only the thick myofilament. It is helpful in the formation of strong skeleton muscle and can also stronger and formation the cardiac layers (epicardium, myocardium and endocardium). Technologically, it can be used in the formation of different food products for the purpose of developing diet supplements. This review discussed different sources and chemical properties of myofibril protein and also its potential role toward the cardiac health. Myofibril’s thick and thin filaments contribute in the construction of skeletal muscle and enhance the heart’s protective coverings. The literature has been collected from Science Direct, Google Scholar and Web of Science. Myofibrils are made up of thick and thin filaments that can help in different human body functions. In the future, more research is necessary that discuss the close relation between myofibril protein and cardiac layers.

Copyright of Food Research & Development is the property of Food Research & Development Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plectin, a highly versatile cytolinker protein, is crucial for myofiber integrity and function. Accordingly, mutations in the human gene (PLEC) cause several rare diseases, denoted as plectinopathies, with most of them associated with progressive muscle weakness. Of several plectin isoforms expressed in skeletal muscle and the heart, P1d is the only isoform expressed exclusively in these tissues. Using high-resolution stimulated emission depletion (STED) microscopy, here we show that plectin is located within the gaps between individual α-actinin-positive Z-disks, recruiting and bridging them to desmin intermediate filaments (Ifs). Loss of plectin in myofibril bundles led to a complete loss of desmin Ifs. Loss of Z-disk-associated plectin isoform P1d led to disorganization of muscle fibers and slower relaxation of myofibrils upon mechanical strain, in line with an observed inhomogeneity of muscle ultrastructure. In addition to binding to α-actinin and thereby providing structural support, P1d forms a scaffolding platform for the chaperone-assisted selective autophagy machinery (CASA) by directly interacting with HSC70 and synpo2. In isoform-specific knockout (P1d-KO) mouse muscle and mechanically stretched plectin-deficient myoblasts, we found high levels of undigested filamin C, a bona fide substrate of CASA. Similarly, subjecting P1d-KO mice to forced swim tests led to accumulation of filamin C aggregates in myofibers, highlighting a specific role of P1d in tension-induced proteolysis activated upon high loads of physical exercise and muscle contraction. [ABSTRACT FROM AUTHOR]

Myosin is the most abundant protein in muscle, accounting for 60% of the total myofibril protein. Myosin can improve water retention and tenderness of meat products, enhance the stability of fat emulsion, and improve the quality of meat gel products, thereby playing significant roles in the processing of meat products. However, myosin is usually bound inside the thick myofilament of the myofibril, Thus, myosin needs to be dissociated from the myofibril in order to play its full role. This paper provides an overview of the effects of actomyosin dissociation on the quality of processed meat products, and on this basis, the dissociation mechanism of actomyosin is further discussed. Meanwhile, the factors affecting the dissociation of actomyosin such as the temperature, pH salt and pyrophosphate used during the processing were examined and summarized, which provides new ideas for meat processing and lays a foundation for improving the quality of processed meat products. [ABSTRACT FROM AUTHOR]

Myosin plays a fundamental role in muscle contraction. Approximately 300 myosins form a bipolar thick filament, in which myosin is continuously replaced by protein turnover. However, it is unclear how rapidly this process occurs and whether the myosin exchange rate differs depending on the region of the thick filament. To answer this question, we first measured myosin release and insertion rates over a short period and monitored myotubes expressing a photoconvertible fluorescence protein‐tagged myosin, which enabled us to monitor myosin release and insertion simultaneously. About 20% of myosins were replaced within 10 min, while 70% of myosins were exchanged over 10 h with symmetrical and biphasic alteration of myosin release and insertion rates. Next, a fluorescence pulse‐chase assay was conducted to investigate whether myosin is incorporated into specific regions in the thick filament. Newly synthesized myosin was located at the tip of the thick filament rather than the center in the first 7 min of pulse‐chase labeling and was observed in the remainder of the thick filament by 30 min. These results suggest that the myosin replacement rate differs depending on the regions of the thick filament. We concluded that myosin release and insertion occur concurrently and that myosin is more frequently exchanged at the tip of the thick filament.

This study was undertaken to evaluate the impact of proteases inactivation on the textural properties of yellow-feathered chicken (YFC) meat and explore the underlying mechanism driving these changes. The results showed that firmness and shelf life of the YFC meat were significantly improved by the proteases inactivation pretreatment in a dose-dependent manner. Specially, the 40% and 60% residual protease activities were identified to yield textures comparable to the hot-fresh YFC meat. Hydration and water retention of the proteases inactivated YFC meat were also found to be enhanced. Further analysis of myofibrillar protein (MP) revealed that cross-linkages of MP were induced by proteases inactivation with 40% and 60%, evidenced by higher levels of disulfide, carbonyl-amine bonds and di-tyrosine. Additionally, the chemical changes in amino acid residues led to the sequestration of tryptophan residues and the formation of β-sheet structures, accompanied by increased turbidity and particle size of MP. Moreover, water holding capacity, lightness, digestibility and strength of the MP gel were found to be improved. The results would provide insights into potential application of proteases inactivation as a strategy to improve YFC textural quality. • Textural quality of cold-stored yellow-feathered chicken was improved and shelf life was extended. • Proteases inactivation enhanced moisture retention and water stability. • Cross-linkage via disulfide and carbonyl bond in myofibrillar protein (MP) was promoted. • Proteases inactivation induced the burial of tryptophan residues and formation of β-sheet in MP. • Water holding capacity, lightness, digestibility, and strength of MP gel were improved. [ABSTRACT FROM AUTHOR]

The maintenance of skeletal muscle mass plays a fundamental role in health and issues associated with quality of life. Mechanical signals are one of the most potent regulators of muscle mass, with a decrease in mechanical loading leading to a decrease in muscle mass. This concept has been supported by a plethora of human- and animal-based studies over the past 100 years and has resulted in the commonly used term of ‘disuse atrophy’. These same studies have also provided a great deal of insight into the structural adaptations that mediate disuse-induced atrophy. For instance, disuse results in radial atrophy of fascicles, and this is driven, at least in part, by radial atrophy of the muscle fibers. However, the ultrastructural adaptations that mediate these changes remain far from defined. Indeed, even the most basic questions, such as whether the radial atrophy of muscle fibers is driven by the radial atrophy of myofibrils and/or myofibril hypoplasia, have yet to be answered. In this review, we thoroughly summarize what is known about the macroscopic, microscopic, and ultrastructural adaptations that mediated disuse-induced atrophy and highlight some of the major gaps in knowledge that need to be filled.

Copyright of Food Research & Development is the property of Food Research & Development Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: Myosin is a molecular motor protein that is critical for using stored energy to yield contraction in both skeletal muscle and in the heart. Mutations in myosin can result in inherited human hypertrophic cardiomyopathy, wherein the heart walls become thickened. This results in inability to adequately pump enough oxygenated blood to meet bodily demands, and can lead to abnormal heart beating patterns and the possibility of sudden death. Typically, over-active myosin can be causative for this disease. Here, we used the common fruit fly to study one of these cardiomyopathy-causing mutations by expressing the mutant protein in the indirect flight muscle of the fly. Surprisingly, we found that the mutation and associated mutations decrease myosin and muscle function instead of enhancing it. We show that at least some of these defects result from improper interactions within the myosin protein. This suggests that appropriate communications within myosin are critical for its function and further indicates that certain aspects of indirect flight muscle myosin are functionally distinct from those of myosin in the human heart. By understanding the intricate interactions within the myosin motor protein that are important for its normal role, therapeutics for improving mutant myosin function can be developed. The R249Q mutation in human β-cardiac myosin results in hypertrophic cardiomyopathy. We previously showed that inserting this mutation into Drosophila melanogaster indirect flight muscle myosin yields mechanical and locomotory defects. Here, we use transgenic Drosophila mutants to demonstrate that residue R249 serves as a critical communication link within myosin that controls both ATPase activity and myofibril integrity. R249 is located on a β-strand of the central transducer of myosin, and our molecular modeling shows that it interacts via a salt bridge with D262 on the adjacent β-strand. We find that disrupting this interaction via R249Q, R249D or D262R mutations reduces basal and actin-activated ATPase activity, actin in vitro motility and flight muscle function. Further, the R249D mutation dramatically affects myofibril assembly, yielding abnormalities in sarcomere lengths, increased Z-line thickness and split myofibrils. These defects are exacerbated during aging. Re-establishing the β-strand interaction via a R249D/D262R double mutation restores both basal ATPase activity and myofibril assembly, indicating that these properties are dependent upon transducer inter-strand communication. Thus, the transducer plays an important role in myosin function and myofibril architecture. [ABSTRACT FROM AUTHOR]

Skeletal muscle consists of slow and fast myofibers in which different myosin isoforms are expressed. Approximately 300 myosins form a single-thick filament in the myofibrils, where myosin is continuously exchanged. However, endogenous slow and fast myosin dynamics have not been fully understood. To elucidate those dynamics, here we generated mice expressing green fluorescence protein-tagged slow myosin heavy chain (GFP-Myh7) and Kusabira Orange fluorescence protein-tagged fast myosin heavy chain (KuO-Myh1). First, these mice enabled us to distinguish between GFP- and KuO-myofibers under fluorescence microscopy: GFP-Myh7 and KuO-Myh1 were exclusively expressed in slow myofibers and fast myofibers, respectively. Next, to monitor endogenous myosin dynamics, fluorescence recovery after photobleaching (FRAP) was conducted. The mobile fraction (Mf) of GFP-Myh7 and that of KuO-Myh1 were almost constant values independent of the regions of the myofibers and the muscle portions where the myofibers were isolated. Intriguingly, proteasome inhibitor treatment significantly decreased the Mf in GFPMyh7 but not in KuO-Myh1 myofibers, indicating that the response to a disturbance in protein turnover depended on muscle fiber type. Taken together, the present results indicated that the mice we generated are promising tools not only for distinguishing between GFP- and KuO-myofibers but also for studying the dynamics of endogenous myosin isoforms by live-cell fluorescence imaging. [ABSTRACT FROM AUTHOR]

The objective of this study was to reveal the effects of boiling processing on the texture of scallop adductor muscle (SAM) and its mechanism. Compared to the fresh sample, all the texture indicators, including the hardness, chewiness, springiness, resilience, cohesiveness, and shear force of 30-s- and 3-min-boiled SAMs increased time-dependently (p < 0.05). As the boiling time increased further to 15 min, the shear force and cohesiveness still increased significantly (p < 0.05), and the resilience and hardness were maintained (p > 0.05), but the springiness and chewiness decreased significantly (p < 0.05). The overall increase in the texture indicators of the boiled SAMs was due to the boiling-induced protein denaturation, aggregation, and increased hydrophobicity, resulting in the longitudinal contraction and lateral expansion of myofibrils, the longitudinal contraction and lateral cross-linked aggregation of muscle fibers, and the loss of free water. However, the decreasing springiness and chewiness of the 15-min-boiled SAMs was due to the significant degradation of proteins (especially collagen), resulting in the destruction of the connective tissue between the muscle fiber clusters. Both from a subjective sensory point of view and from the objective point of view of protein denaturation and degradation, 3-min-boiled SAMs are recommended. The quality improvement of thermally processed products by controlled, moderate cooking is of practical value from the perspective of food consumption. [ABSTRACT FROM AUTHOR]

Human muscle is a hierarchically organised tissue with its contractile cells called myofibers packed into large myofiber bundles. Each myofiber contains periodic myofibrils built by hundreds of contractile sarcomeres that generate large mechanical forces. To better understand the mechanisms that coordinate human muscle morphogenesis from tissue to molecular scales, we adopted a simple in vitro system using induced pluripotent stem cell-derived human myogenic precursors. When grown on an unrestricted two-dimensional substrate, developing myofibers spontaneously align and self-organise into higher-order myofiber bundles, which grow and consolidate to stable sizes. Following a transcriptional boost of sarcomeric components, myofibrils assemble into chains of periodic sarcomeres that emerge across the entire myofiber. More efficient myofiber bundling accelerates the speed of sarcomerogenesis suggesting that tension generated by bundling promotes sarcomerogenesis. We tested this hypothesis by directly probing tension and found that tension build-up precedes sarcomere assembly and increases within each assembling myofibril. Furthermore, we found that myofiber ends stably attach to other myofibers using integrin-based attachments and thus myofiber bundling coincides with stable myofiber bundle attachment in vitro. A failure in stable myofiber attachment results in a collapse of the myofibrils. Overall, our results strongly suggest that mechanical tension across sarcomeric components as well as between differentiating myofibers is key to coordinate the multi-scale self-organisation of muscle morphogenesis.

The short shelf-life of shrimp due to microbial activity and protein spoilage poses a threaten for preservation. In this study, the preservation effect of slightly acid electrolysed water (SAEW) combined with grape seed extract (GSE) was investigated. The combined treatment effectively inhibited the growth of spoilage bacteria including Aeromonas , Pseudomonas , Shewanella , and Enterobacteriaceae, which accounted for shrimp spoilage. Besides, the combination efficiently preserved the shrimp colour during storage. To further elucidate the preservative mechanism, the proteomic analysis was conducted, a total of 47 different abundant proteins (DAPs) were identified and quantified. Among these, the combination treatment was most effective in maintaining the main structural proteins presented in myofibrillar protein of shrimp including myosin heavy chain, myosin light chain, actin, and projectin, which was verified by the least changes in texture and protein morphology in combination treated shrimp after storage. These results provided proteomics insight for the preservative mechanism of combined usage of SAEW and GSE. [Display omitted] • Slightly acid electrolysed water with grape seed extract preserved shrimp quality. • A total of 47 different abundant proteins were identified and quantified. • Combination treated shrimp showed the least structural proteome changes. • Myosin, projectin, and actin were maintained by combined treatment. [ABSTRACT FROM AUTHOR]

Plectin, a highly versatile cytolinker protein, is crucial for myofiber integrity and function. Accordingly, mutations in the human gene (PLEC) cause several rare diseases, denoted as plectinopathies, with most of them associated with progressive muscle weakness. Of several plectin isoforms expressed in skeletal muscle and the heart, P1d is the only isoform expressed exclusively in these tissues. Using high-resolution stimulated emission depletion (STED) microscopy, here we show that plectin is located within the gaps between individual α-actinin-positive Z-disks, recruiting and bridging them to desmin intermediate filaments (Ifs). Loss of plectin in myofibril bundles led to a complete loss of desmin Ifs. Loss of Z-disk-associated plectin isoform P1d led to disorganization of muscle fibers and slower relaxation of myofibrils upon mechanical strain, in line with an observed inhomogeneity of muscle ultrastructure. In addition to binding to α-actinin and thereby providing structural support, P1d forms a scaffolding platform for the chaperone-assisted selective autophagy machinery (CASA) by directly interacting with HSC70 and synpo2. In isoform-specific knockout (P1d-KO) mouse muscle and mechanically stretched plectin-deficient myoblasts, we found high levels of undigested filamin C, a bona fide substrate of CASA. Similarly, subjecting P1d-KO mice to forced swim tests led to accumulation of filamin C aggregates in myofibers, highlighting a specific role of P1d in tension-induced proteolysis activated upon high loads of physical exercise and muscle contraction.

Meat is the richest source of protein and according to meat sources, the protein is composed of different types of amino acids which are completely dependent upon the protein types. Myofibril is basically muscle protein that's widely present in different types of fish and low quantity is present in different meat (camel). Myofibril is made up of thick and thin myofilaments chemically. Actin, tropomyosin, troponin, and tropomyosin are thin myofilaments on the other hand myosin is only the thick myofilament. It is helpful in the formation of strong skeleton muscle and can also stronger and formation the cardiac layers (epicardium, myocardium and endocardium). Technologically, it can be used in the formation of different food products for the purpose of developing diet supplements. This review discussed different sources and chemical properties of myofibril protein and also its potential role toward the cardiac health. Myofibril's thick and thin filaments contribute in the construction of skeletal muscle and enhance the heart's protective coverings. The literature has been collected from Science Direct, Google Scholar and Web of Science. Myofibrils are made up of thick and thin filaments that can help in different human body functions. In the future, more research is necessary that discuss the close relation between myofibril protein and cardiac layers. [ABSTRACT FROM AUTHOR]

Wanrui Ma,1,2 Shan He,3 Yanping Xu,4 Guoxue Qi,3 Huiyan Ma,3 John J Bang,5 P Andy Li2 1Department of General Medicine, General Hospital of Ningxia Medical University, Yinchuan, Ningxia, People’s Republic of China; 2Department of Pharmaceutical Sciences, Biomanufacturing Research Institute and Technological Enterprise (BRITE), North Carolina Central University, Durham, NC, USA; 3Ningxia Medical University, Yinchuan, Ningxia, People’s Republic of China; 4Unit of Echocardiography, Division of Functional Examination in Heart Center, General Hospital of Ningxia Medical University, Yinchuan, Ningxia, People’s Republic of China; 5Department of Environmental, Earth and Geospatial Sciences, North Carolina Central University, Durham, NC, USACorrespondence: P Andy LiDepartment of Pharmaceutical Sciences, Biomanufacturing Research Institute and Technological Enterprise (BRITE), North Carolina Central University, 1801 Fayetteville Street, Durham, NC 27707, USATel +1 919 530 6872Fax +1 919 530 6600Email pli@nccu.eduBackground: The application of silver nanoparticles (AgNPs) is growing exponentially, and its potential damage to the cardiac remains to be elucidated. The purpose of this study was to investigate the ameliorative effect of sodium selenite on silver nanoparticles-induced myocardiocyte structural alterations in rats.Materials and Methods: Forty male Sprague-Dawley (SD) rats were randomly divided into four groups: control group, AgNPs group, Se control group, and AgNPs + Se group. SD rats were administered AgNPs through a single intratracheal instillation, and sodium selenite was given by intraperitoneal injection for seven days. Cardiac function was determined by echocardiography and hemodynamic, ultrastructural changes by transmission electron microscopy examination. Mitochondrial fission and autophagy markers were measured by Western blotting.Results: AgNPs caused a significant decrease in cardiac contraction, diastolic dysfunction, fragmentation, and lysis of the myofibrils, the formation of stenosis in the capillary, damaging the mitochondria membrane and cristae. AgNPs significantly increased mitochondrial fission markers dynamin-related protein 1 (Drp1), phospho-Drp1 (p-Drp1), and mitochondrial fission protein 1 (Fis1), as well as autophagy marker LC3 II/I (P< 0.05). Treatment with sodium selenite is capable of protecting cardiac function from AgNPs toxicity through attenuating ultrastructural alterations, stabilizing mitochondrial dynamic balance and blocking mitochondrial autophagy.Conclusion: We conclude that the protection of sodium selenite against silver nanoparticles-induced myocardiocyte structural alterations is associated with stabilizing mitochondrial dynamic balance and mitophagy.Keywords: heart, mitochondria, mitochondrial fission, myocardiocyte, myofibril, sarcomere, silver nanoparticles, sodium selenite

Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.

New Findings: What is the main observation in this case?The main observation of this case report is that blood flow‐restricted exercise can cause myofibrils to have an aberrant wave‐like appearance that is accompanied by irregular pockets of sarcoplasm in the intermyofibrillar space, while traditional forms of damage to the Z‐discs and contractile elements are not as apparent.What insights does it reveal?Our findings indicate that blood flow restriction‐mediated fluid pooling might cause alterations in skeletal muscle ultrastructure after exercise that might be directly related to myofibre swelling. The acute effects of blood flow‐restricted (BFR) exercise training on skeletal muscle ultrastructure are poorly understood owing to inconsistent findings and the use of largely imprecise systemic markers for indications of muscle damage. The purpose of this study was to compare myofibrillar ultrastructure before and 30 min after normal and BFR resistance exercise using transmission electron microscopy in a single individual to evaluate the feasibility of this more nuanced approach. One apparently healthy male with 13 years of resistance exercise completed six sets of both BFR [30% of one‐repetition maximum (1‐RM)] and normal non‐occluded (70% of 1‐RM) unilateral angled leg press on the contralateral leg, as a control, after assessment of 1‐RM 72 h before. Vastus lateralis muscle biopsies were collected before and 30 min after each exercise session. The lengths and widths of 250 sarcomeres and the sarcoplasmic area were assessed via 20 individual transmission electron photomicrographs. Analysis revealed that BFR training (1.769 ± 0.12 μm) increased sarcomere length when compared with normal exercise (1.64 ± 0.17 μm; P < 0.001), without differences in sarcomere width between conditions (BFR, 0.90 ± 0.26 μm; normal, 0.93 ± 0.27 μm; P = 0.172). Furthermore, there were no significant interaction (P = 0.168) or condition effects between BFR (25.98 ± 4.17%) and normal (27.3 ± 6.49%) resistance exercise for sarcoplasmic area (P = 0.229). Exercise also increased sarcoplasmic area within the myofibril (pre‐exercise, 24.42 ± 5.13%; postexercise, 28.95 ± 5.92%) for both conditions (P = 0.001). This case study demonstrates a unique BFR training‐induced alteration in myofibril ultrastructure that appeared wave like and was accompanied by intracellular abnormalities that appeared to be fluid pockets of sarcoplasm disrupting the surrounding myofibrils. [ABSTRACT FROM AUTHOR]

In this study, we analyze radiation images of muscle structure of mice soleus muscles using radiation source‐based microtomography and nanotomography. Soleus muscle samples were collected for analysis from 8‐week‐old male Institute of Cancer Research mice. First, phase‐contrast X‐ray microtomography was employed in these experiments. Then to obtain images with excellent contrast, imaging was performed using monochromatic light with excellent transmission power. To analyze additional muscle structures in higher magnification images than these images, nanotomography was performed, which facilitated obtaining high‐magnification and high‐resolution images. Muscle tissue microstructures were confirmed through three‐dimensional images obtained from phase‐contrast X‐ray microtomography. Thus, the muscle tissue's overall shape at microscopic level can be captured. Additionally, a single muscle fiber was examined using hard X‐ray nano‐imaging, through which we could observe the alignment of countless myofibrils, that is, actin and myosin filaments in the muscle fibers. Thus, the methodology adopted here proved to be advantageous in analyzing the muscle tissue's overall structure with microtomography and in observing the myofibrils in detail using nanotomography. [ABSTRACT FROM AUTHOR]

Two hypertrophic cardiomyopathy-associated cardiac troponin I (cTnI) mutations, R146G and R21C, are located in different regions of cTnI, the inhibitory peptide and the cardiac-specific N terminus. We recently reported that these regions may interact when Ser-23/Ser-24 are phosphorylated, weakening the interaction of cTnI with cardiac TnC. Little is known about how these mutations influence the affinity of cardiac TnC for cTnI (KC-I) or contractile kinetics during β-adrenergic stimulation. Here, we tested how cTnI(R146G) or cTnI(R21C) influences contractile activation and relaxation and their response to protein kinase A (PKA). Both mutations significantly increased Ca(2+) binding affinity to cTn (KCa) and KC-I. PKA phosphorylation resulted in a similar reduction of KCa for all complexes, but KC-I was reduced only with cTnI(WT). cTnI(WT), cTnI(R146G), and cTnI(R21C) were complexed into cardiac troponin and exchanged into rat ventricular myofibrils, and contraction/relaxation kinetics were measured ± PKA phosphorylation. Maximal tension (Tmax) was maintained for cTnI(R146G)- and cTnI(R21C)-exchanged myofibrils, and Ca(2+) sensitivity of tension (pCa50) was increased. PKA phosphorylation decreased pCa50 for cTnI(WT)-exchanged myofibrils but not for either mutation. PKA phosphorylation accelerated the early slow phase relaxation for cTnI(WT) myofibrils, especially at Ca(2+) levels that the heart operates in vivo. Importantly, this effect was blunted for cTnI(R146G)- and cTnI(R21C)-exchanged myofibrils. Molecular dynamics simulations suggest both mutations inhibit formation of intra-subunit contacts between the N terminus and the inhibitory peptide of cTnI that is normally seen with WT-cTn upon PKA phosphorylation. Together, our results suggest that cTnI(R146G) and cTnI(R21C) blunt PKA modulation of activation and relaxation kinetics by prohibiting cardiac-specific N-terminal interaction with the cTnI inhibitory peptide.

Abstract Myosin, the most abundant myofibrillar protein in skeletal muscle, functions as a motor protein in muscle contraction. Myosin polymerizes into the thick filaments in the sarcomere where approximately 50% of embryonic myosin (Myh3) are replaced within 3 h (Ojima K, Ichimura E, Yasukawa Y, Wakamatsu J, Nishimura T, Am J Physiol Cell Physiol 309: C669‐C679, 2015). The sarcomere structure including the thick filament is maintained by a balance between protein biosynthesis and degradation. However, the involvement of a protein degradation system in the myosin replacement process remains unclear. Here, we show that the muscle‐specific ubiquitin ligase Ozz regulates replacement rate of Myh3. To examine the direct effect of Ozz on myosin replacement, eGFP‐Myh3 replacement rate was measured in myotubes overexpressing Ozz by fluorescence recovery after photobleaching. Ozz overexpression significantly decreased the replacement rate of eGFP‐Myh3 in the myofibrils, whereas it had no effect on other myosin isoforms. It is likely that ectopic Ozz promoted myosin degradation through increment of ubiquitinated myosin, and decreased myosin supply for replacement, thereby reducing myosin replacement rate. Intriguingly, treatment with a proteasome inhibitor MG132 also decreased myosin replacement rate, although MG132 enhanced the accumulation of ubiquitinated myosin in the cytosol where replaceable myosin is pooled, suggesting that ubiquitinated myosin is not replaced by myosin in the myofibril. Collectively, our findings showed that Myh3 replacement rate was reduced in the presence of overexpressed Ozz probably through enhanced ubiquitination and degradation of Myh3 by Ozz.

Myosin, the most abundant myofibrillar protein in skeletal muscle, functions as a motor protein in muscle contraction. Myosin polymerizes into the thick filaments in the sarcomere where approximately 50% of embryonic myosin (Myh3) are replaced within 3 h (Ojima K, Ichimura E, Yasukawa Y, Wakamatsu J, Nishimura T, Am J Physiol Cell Physiol 309: C669‐C679, 2015). The sarcomere structure including the thick filament is maintained by a balance between protein biosynthesis and degradation. However, the involvement of a protein degradation system in the myosin replacement process remains unclear. Here, we show that the muscle‐specific ubiquitin ligase Ozz regulates replacement rate of Myh3. To examine the direct effect of Ozz on myosin replacement, eGFP‐Myh3 replacement rate was measured in myotubes overexpressing Ozz by fluorescence recovery after photobleaching. Ozz overexpression significantly decreased the replacement rate of eGFP‐Myh3 in the myofibrils, whereas it had no effect on other myosin isoforms. It is likely that ectopic Ozz promoted myosin degradation through increment of ubiquitinated myosin, and decreased myosin supply for replacement, thereby reducing myosin replacement rate. Intriguingly, treatment with a proteasome inhibitor MG132 also decreased myosin replacement rate, although MG132 enhanced the accumulation of ubiquitinated myosin in the cytosol where replaceable myosin is pooled, suggesting that ubiquitinated myosin is not replaced by myosin in the myofibril. Collectively, our findings showed that Myh3 replacement rate was reduced in the presence of overexpressed Ozz probably through enhanced ubiquitination and degradation of Myh3 by Ozz. [ABSTRACT FROM AUTHOR]

Background: Flying is an essential function for mosquitoes, required for mating and, in the case of females, to get a blood meal and consequently function as a vector. Flight depends on the action of the indirect flight muscles (IFMs), which power the wings beat. No description of the development of IFMs in mosquitoes, including Aedes aegypti, is available. Methods: A. aegypti thoraces of larvae 3 and larvae 4 (L3 and L4) instars were analyzed using histochemistry and bright field microscopy. IFM primordia from L3 and L4 and IFMs from pupal and adult stages were dissected and processed to detect F-actin labelling with phalloidin-rhodamine or TRITC, or to immunodetection of myosin and tubulin using specific antibodies, these samples were analyzed by confocal microscopy. Other samples were studied using transmission electron microscopy. Results: At L3–L4, IFM primordia for dorsal-longitudinal muscles (DLM) and dorsal–ventral muscles (DVM) were identified in the expected locations in the thoracic region: three primordia per hemithorax corresponding to DLM with anterior to posterior orientation were present. Other three primordia per hemithorax, corresponding to DVM, had lateral position and dorsal to ventral orientation. During L3 to L4 myoblast fusion led to syncytial myotubes formation, followed by myotendon junctions (MTJ) creation, myofibrils assembly and sarcomere maturation. The formation of Z-discs and M-line during sarcomere maturation was observed in pupal stage and, the structure reached in teneral insects a classical myosin thick, and actin thin filaments arranged in a hexagonal lattice structure. Conclusions: A general description of A. aegypti IFM development is presented, from the myoblast fusion at L3 to form myotubes, to sarcomere maturation at adult stage. Several differences during IFM development were observed between A. aegypti (Nematoceran) and Drosophila melanogaster (Brachyceran) and, similitudes with Chironomus sp. were observed as this insect is a Nematoceran, which is taxonomically closer to A. aegypti and share the same number of larval stages. [ABSTRACT FROM AUTHOR]

Sarcomere, compartmentalization, concentration, subcellular localization, CUTie sensor, cyclic nucleotide, myofibril, nanodomain Its diffusion is limited by phosphodiesterases (PDEs), which convert it to AMP.[1] The holotetrameric protein kinase A (PKA) constitutes a primary effector of cAMP. A 30 nm ruler is added to facilitate the comparison with panel A. (C) Cartoon representations of skeletal and cardiac muscle troponin systems colored as in B. The protein segment proposed as AKAP in the cardiac TnT is shown with all-atoms representation, and the helix-breaking proline residue in the skeletal TnT is highlighted. Keywords: sarcomere; cyclic nucleotide; compartmentalization; concentration; subcellular localization; CUTie sensor; myofibril; nanodomain EN sarcomere cyclic nucleotide compartmentalization concentration subcellular localization CUTie sensor myofibril nanodomain 1 3 3 10/21/22 20220901 NES 220901 Intracellular signaling is often conceptualized as a series of processes triggered by increasing/decreasing concentrations of small molecules. [Extracted from the article]

Protein hydrolysates contain bioactive peptides which have several function in order to maintain health and reduce the risk of disease. One of the functions of bioactive peptides is as an antioxidant. This study aims to characterize eel myofibril (Synbranchus bengalensis), determine the effect of papain enzyme ratio and hydrolysis time on eel myofibril protein hydrolysates, determine the antioxidant activity of eel myofibril hydrolysates by using DPPH and reducing power assay, and characterize the hydrolysate of myofibril proteins which have the best antioxidant activity. The results showed that eel myofibril protein contained moisture, fat, protein and ash of 85.91, 0.15, 0.14 and 12.78% respectively and contained the highest glutamic acid and lysine. Hydrolysates of eel myofibril proteins treated using various enzyme ratio and hydrolysis time had hydrolysates yields ranging from 3.53-9.68%, the value of hydrolysis degrees 5.20 - 16.193%, IC50 14.24 - 30.26 mg/mL for DPPH assay and absorbance 0.125 - 0.190 at a concentration of 5 mg/mL for reducing power assay. Hydrolysis eel myofibril protein using ratio papain 0.20:100 for 2 hours produced the highest antioxidant activities measuring by DPPH scavenging and reducing power iron. The hydrolysate had molecular weight approximately 19.51 kDa. Glutamic acid and lysine became the dominant amino acids of the hydrolysate.

The R249Q mutation in human β-cardiac myosin results in hypertrophic cardiomyopathy. We previously showed that inserting this mutation into Drosophila melanogaster indirect flight muscle myosin yields mechanical and locomotory defects. Here, we use transgenic Drosophila mutants to demonstrate that residue R249 serves as a critical communication link within myosin that controls both ATPase activity and myofibril integrity. R249 is located on a β-strand of the central transducer of myosin, and our molecular modeling shows that it interacts via a salt bridge with D262 on the adjacent β-strand. We find that disrupting this interaction via R249Q, R249D or D262R mutations reduces basal and actin-activated ATPase activity, actin in vitro motility and flight muscle function. Further, the R249D mutation dramatically affects myofibril assembly, yielding abnormalities in sarcomere lengths, increased Z-line thickness and split myofibrils. These defects are exacerbated during aging. Re-establishing the β-strand interaction via a R249D/D262R double mutation restores both basal ATPase activity and myofibril assembly, indicating that these properties are dependent upon transducer inter-strand communication. Thus, the transducer plays an important role in myosin function and myofibril architecture.

Skeletal muscles are composed of gigantic cells called muscle fibers, packed with force-producing myofibrils. During development, the size of individual muscle fibers must dramatically enlarge to match with skeletal growth. How muscle growth is coordinated with growth of the contractile apparatus is not understood. Here, we use the large Drosophila flight muscles to mechanistically decipher how muscle fiber growth is controlled. We find that regulated activity of core members of the Hippo pathway is required to support flight muscle growth. Interestingly, we identify Dlg5 and Slmap as regulators of the STRIPAK phosphatase, which negatively regulates Hippo to enable post-mitotic muscle growth. Mechanistically, we show that the Hippo pathway controls timing and levels of sarcomeric gene expression during development and thus regulates the key components that physically mediate muscle growth. Since Dlg5, STRIPAK and the Hippo pathway are conserved a similar mechanism may contribute to muscle or cardiomyocyte growth in humans.

Background: To identify novel myofibrillar components of the Drosophila flight muscles, we carried out a proteomic analysis of chemically demembranated flight muscle myofibrils, and characterized the knockdown phenotype of a novel gene identified in the screen, CG1674. Results: The CG1674 protein has some similarity to vertebrate synaptopodin 2‐like, and when expressed as a FLAG‐tagged fusion protein, it was localized during development to the Z‐disc and cytoplasm. Knockdown of CG1674 expression affected the function of multiple muscle types, and defective flight in adults was accompanied by large actin‐rich structures in the flight muscles that resembled overgrown Z‐discs. Localization of CG1674 to the Z‐disc depended predominantly upon presence of the Z‐disc component alpha‐actinin, but also depended upon other Z‐disc components, including Mask, Zasp52, and Sals. We also observed re‐localization of FLAG‐CG1674 to the nucleus in Alpha‐actinin and sals knockdown animals. Conclusions: These studies identify and characterize a previously unreported myofibrillar component of Drosophila muscle that is necessary for proper myofibril assembly during development. Key Findings: We characterize the Drosophila flight muscle myofibril proteomeWe identify a novel myofibrillar component, CG1674CG1674 localizes to the Z‐discKnockdown of CG1674 results in actin‐rich structures in the muscle [ABSTRACT FROM AUTHOR]