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Fission yeast Schizosaccharomyces pombe serves as model organism for studying higher eukaryotes. We combined the use of cryo-EM and spectroscopy to investigate the structure and function of affinity purified respiratory complex IV (CIV) from S. pombe. The reaction sequence of the reduced enzyme with O 2 proceeds over a time scale of µs-ms, similar to that of the mammalian CIV. The cryo-EM structure of CIV revealed eleven subunits as well as a bound hypoxia-induced gene 1 (Hig1) domain of respiratory supercomplex factor 2 (Rcf2). These results suggest that binding of Rcf2 does not require the presence of a CIII-CIV supercomplex, i.e. Rcf2 is a component of CIV. An AlphaFold-Multimer model suggests that the Hig1 domains of both Rcf1 and Rcf2 bind at the same site of CIV suggesting that their binding is mutually exclusive. Furthermore, the differential functional effect of Rcf1 or Rcf2 is presumably caused by interactions of CIV with their different non-Hig1 domain parts., (© 2023. The Author(s).)

Light-induced structural changes in photosynthetic reaction centers from Rhodobacter sphaeroides were investigated using two approaches. Cu2+ was used as a paramagnetic structural probe. The EPR spectrum of Cu2+ incorporated into the metal-depleted reaction centers was affected by 1,10-phenanthroline, an electron transfer inhibitor substituting QB, which suggests a localization of Cu2+ in a vicinity of the Q site. However, the spectrum was not influenced by low temperature (77 K) illumination of the sample which suggests that the copper ion position is not exactly the same as that of the iron ion. Freezing the reaction centers under illumination in the presence of potassium ferricyanide and 1,10-phenanthroline caused a change in the shape of the Cu2+ EPR spectrum in comparison to that of a sample frozen in darkness. These data indicate a change of the Cu2+ ligand symmetry owing to light-induced structural changes which are probably located near the acceptor side of the reaction center. Partial trypsinolysis of reaction centers was also used to locate the structural changes. Trypsin treatment in the dark and under illumination resulted in different peptide patterns as detected by gel electrophoresis and reverse-phase high-performance liquid chromatography. Partial amino-acid sequence analysis of a number of peptides, characteristic of either light- or dark-treated reaction centers, showed that they originated from the acceptor sides of the H and M subunits. The occurrence of light-induced structural differences in the H-subunit is consistent with the suggestion that it may be involved in regulating electron transfer in this part of the reaction center. [ABSTRACT FROM AUTHOR]

Reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides were oriented in phospholipid interfacial layers adsorbed to a Teflon film separating two electrolyte-filled compartments of a Teflon cell. Light-induced voltage changes were measured as a function of time across electrodes immersed in the cell compartments. The experimental system is characterized both experimentally and theoretically to relate the measured signals to the light-induced displacement currents in the reaction centers. Mathematical relations between the measured signals and the distances and geometries of the charge-transfer reactions are derived. At pH 8.0 the reaction centers were found to be oriented with approximately 60% of the population oriented with the donor facing the aqueous phase. The density of the reaction centers in the layer was approximately 10(11) cm-2, which is close to that found in the native system. Reconstitution of the secondary quinone, QB, in 90% of the RCs was achieved with an approximately 100-fold excess of ubiquinone in the vesicle preparation. [ABSTRACT FROM AUTHOR]

The hair follicles of recipients of allogeneic hematopoietic SCT (HSCT) constitute the tissue with the greatest need for regeneration after high-dose chemotherapy. Previous studies have shown a lack of donor-derived DNA in the hair follicles of recipients. Therefore, we carried out a study to determine whether male donor-derived genetic material can be found in female recpients' hair follicles after HSCT. Fluorescent-based PCR with analyses of Y-chromosome STR (Y-STR) and RQ-PCR with the sex-determining region Y (SRY) were used independently to evaluate chimerism status. Our results proved the existence of donor-derived stem DNA in the recipients' hair follicle cells. This report undermines the validity of data indicating that hair follicle cells maintain 100% of recipient origin. [ABSTRACT FROM AUTHOR]

Recent studies have established that cellular electrostatic interactions are more influential than assumed previously. Here, we use cryo-EM and perform steady-state kinetic studies to investigate electrostatic interactions between cytochrome (cyt.) c and the complex (C) III2-IV supercomplex from Saccharomyces cerevisiae at low salinity. The kinetic studies show a sharp transition with a Hill coefficient ≥2, which together with the cryo-EM data at 2.4 Å resolution indicate multiple cyt. c molecules bound along the supercomplex surface. Negatively charged loops of CIII2 subunits Qcr6 and Qcr9 become structured to interact with cyt. c. In addition, the higher resolution allows us to identify water molecules in proton pathways of CIV and, to the best of our knowledge, previously unresolved cardiolipin molecules. In conclusion, the lowered electrostatic screening renders engagement of multiple cyt. c molecules that are directed by electrostatically structured CIII2 loops to conduct electron transfer between CIII2 and CIV. Previous studies have shown that cellular electrostatic interactions are influential. Here the authors use cryo-EM and steady-state kinetic studies to investigate electrostatic interactions between cytochrome (cyt.) c and the complex (C) III2-IV supercomplex from S.cerevisiae at low salinity. [ABSTRACT FROM AUTHOR]

Radiotherapy (RT) is a widely used treatment with strong therapeutic effects, but overcoming challenges related to hypoxia-induced tumor resistance and ineffective antitumor immune responses is crucial for optimal outcomes. In this study, we developed a versatile nanosystem using mesoporous silica nanoparticles (MSNs), R837, and a small quantity of manganese peroxide (Mn/ZnO2). The synthesized MSN@R837-Mn/ZnO2 nanoparticles exhibited precise tumor targeting and accumulation, controlled drug release under acidic conditions, and increased sensitivity in magnetic resonance imaging. These attributes collectively augmented the therapeutic efficacy of RT by alleviating hypoxia and immunosuppression. Tumor cells treated with RT combined with these nanoparticles displayed reduced oxidative stress, alleviated hypoxia, and normalized blood vessel formation. Notably, all mice in the RT + PD-1 + MSN@R837-Mn/ZnO2 group achieved complete tumor regression with extended survival. Safety assessments confirmed the absence of MSN@R837-Mn/ZnO2 toxicity, highlighting its potential as a promising approach with dual functionality for the diagnostic imaging and treatment of cancer. Radiotherapy (RT) faces challenges like hypoxia-induced tumor resistance and weak antitumor immune responses. This study developed a nanosystem using mesoporous silica nanoparticles (MSNs), R837, and manganese peroxide (Mn/ZnO2). The MSN@R837-Mn/ZnO2 nanoparticles showed precise tumor targeting, controlled drug release in acidic conditions, and enhanced MRI sensitivity, boosting RT efficacy by reducing hypoxia and immunosuppression. Tumor cells treated with RT and these nanoparticles had less oxidative stress, improved hypoxia, and normalized blood vessels. Remarkably, all mice in the RT+PD-1+MSN@R837-Mn/ZnO2 group achieved complete tumor regression and extended survival, with no toxicity observed, indicating its potential for cancer imaging and treatment. [ABSTRACT FROM AUTHOR]

The ground state double proton transfer (GSDPT) process of 2-aminopyrazine (APz) complex bonded with one bridged water molecule was investigated in detail at the M06-2X/6-31G(d, p) level. The extra hydrogen bonded (H-bonded) network formed between APz and 1 ~ 3 extra water molecules was drawn into APz-H2O complex to form APz-(H2O)n+m (n = 1, m = 1–3) complexes, and its effects on GSDPT process in APz-H2O were explored systematically. Based on the analyses of structural parameters and correlation plots, we found that the GSDPT reaction occurred in a concerted but asynchronous protolysis or solvolysis pattern depending on the location and number of the extra water molecules. The energy barrier of GSDPT process was also affected by the location and number of the extra water molecules. [ABSTRACT FROM AUTHOR]

Aerobic life is powered by membrane-bound redox enzymes that shuttle electrons to oxygen and transfer protons across a biological membrane. Structural studies suggest that these energy-transducing enzymes operate as higher-order supercomplexes, but their functional role remains poorly understood and highly debated. Here we resolve the functional dynamics of the 0.7 MDa III2IV2 obligate supercomplex from Mycobacterium smegmatis, a close relative of M. tuberculosis, the causative agent of tuberculosis. By combining computational, biochemical, and high-resolution (2.3 Å) cryo-electron microscopy experiments, we show how the mycobacterial supercomplex catalyses long-range charge transport from its menaquinol oxidation site to the binuclear active site for oxygen reduction. Our data reveal proton and electron pathways responsible for the charge transfer reactions, mechanistic principles of the quinone catalysis, and how unique molecular adaptations, water molecules, and lipid interactions enable the proton-coupled electron transfer (PCET) reactions. Our combined findings provide a mechanistic blueprint of mycobacterial supercomplexes and a basis for developing drugs against pathogenic bacteria. The obligate supercomplex from M. Tuberculosis has emerged as a promising drug target. Here the authors employ structural experiments, activity assays, and multiscale molecular simulations, to elucidate the mechanism of charge transfer in this enzyme. [ABSTRACT FROM AUTHOR]

Hidradenitis suppurativa (HS) is a debilitating chronic skin disorder characterized by painful inflammatory nodules, abscesses and sinus tracts involving intertriginous areas and has an adverse impact on patient quality of life. Over the past decade, the therapeutic options of HS have increased significantly to comprise multiple modalities, including topical medication, systemic therapies (mainly antibiotics, retinoids, and biologics), surgical approaches, and lifestyle modifications. Biologics alone or in combination with surgery remain the treatment of choice for moderate to severe disease. However, non-biologic therapies (including retinoids) may be used as monotherapy for mild disease and in combination with biologics and surgical treatment in moderate to severe disease. Retinoids, specifically isotretinoin, acitretin, and alitretinoin, are historically used in the management of HS, supported by anecdotal evidence and with variable treatment response. Although the current American and European guidelines offer different recommendations on the use of retinoids in HS, retinoids remain a valuable ally in HS management. This review provides a comprehensive analysis of the current scientific literature on retinoid therapy (topical and systemic) in HS, highlighting disparities in mechanisms of action, efficacy, and safety to clarify their role in HS treatment. [ABSTRACT FROM AUTHOR]

In cytochrome c oxidase (CytcO) reduction of O2 to water is linked to uptake of eight protons from the negative side of the membrane: four are substrate protons used to form water and four are pumped across the membrane. In bacterial oxidases, the substrate protons are taken up through the K and the D proton pathways, while the pumped protons are transferred through the D pathway. On the basis of studies with CytcO isolated from bovine heart mitochondria, it was suggested that in mitochondrial CytcOs the pumped protons are transferred though a third proton pathway, the H pathway, rather than through the D pathway. Here, we studied these reactions in S. cerevisiae CytcO, which serves as a model of the mammalian counterpart. We analyzed the effect of mutations in the D (Asn99Asp and Ile67Asn) and H pathways (Ser382Ala and Ser458Ala) and investigated the kinetics of electron and proton transfer during the reaction of the reduced CytcO with O2. No effects were observed with the H pathway variants while in the D pathway variants the functional effects were similar to those observed with the R. sphaeroides CytcO. The data indicate that the S. cerevisiae CytcO uses the D pathway for proton uptake and presumably also for proton pumping. [ABSTRACT FROM AUTHOR]

The excited state relaxation dynamics of 2-(2′-hydroxyphenyl)benzothiazole (HBT) in the gas phase and the solvents have been explored experimentally and theoretically. However, the fundamental mechanism of its emission in aggregates is still unexplored. In this article, we have presented a detail investigation of solvent-regulated excited state (ES) reactions for HBT aggregates with the aid of several experimental and theoretical research. The careful investigation of solvatochromic and electrochemical behavior elucidates that the emission around 460 nm of HBT in DMSO and DMSO–water fraction correspond to the excited state internal charge transfer (ESICT). The quantum chemical analysis further supports this observation. The concentration-dependent 1H NMR and emission studies of HBT in DMSO revealed the formation of aggregates at higher concentrations that facilitate the charge transfer. The emission pattern of HBT in the AcN–water fraction demonstrates that the sequential internal charge transfer-proton transfer (ESICT–ESIPT) occurs in HBT aggregates. The pH studies show that HBT aggregates are potential ratiometric sensors for near-physiological pH ranges. Moreover, a ground-state zwitterionic conformation of HBT is observed in the basic medium formed by ground-state internal proton transfer (GSIPT). Overall, this study provides a better understanding of solvent-regulated ES reaction mechanism in the case of HBT aggregates and other substituted HBT compound aggregates published previously. [ABSTRACT FROM AUTHOR]

This article discusses a rare case of intracranial hypertension (IH) that occurred after treatment with isotretinoin for rosacea. IH is a neurological condition characterized by increased intracranial pressure, and it can be a side effect of certain medications. The patient in this case experienced recurring IH under isotretinoin monotherapy and subsequently under doxycycline monotherapy. The article highlights the potential association between isotretinoin and IH, as well as the possible role of a preceding COVID-19 infection in triggering the condition. It also suggests considering secondary causes of persistent headache in patients undergoing isotretinoin treatment and performing a medication review if necessary. [Extracted from the article]

Xerostomia, the subjective sensation of 'dry mouth' affecting at least 1 in 10 adults, predominantly elders, increases life-threatening infections, adversely impacting nutritional status and quality of life. A patented, microgel-reinforced hydrogel-based aqueous lubricant, prepared using either dairy or plant-based proteins, has been demonstrated to offer substantially enhanced lubricity comparable to real human saliva in in vitro experiments. Herein, we present the benchmarking of in vitro lubrication performance of this aqueous lubricant, both in its dairy and vegan formulation against a range of widely available and employed commercial saliva substitutes, latter classified based on their shear rheology into "liquids", "viscous liquids" and "gels", and also had varying extensional properties. Strikingly, the fabricated dairy-based aqueous lubricant offers up to 41–99% more effective boundary lubrication against liquids and viscous liquids, irrespective of topography of the tested dry mouth-mimicking tribological surfaces. Such high lubricity of the fabricated lubricants might be attributed to their limited real-time desorption (7%) from a dry-mouth mimicking hydrophobic surface unlike the tested commercial products including gels (23–58% desorption). This comprehensive benchmarking study therefore paves the way for employing these microgel-based aqueous lubricant formulations as a novel topical platform for dry mouth therapy. [ABSTRACT FROM AUTHOR]

Erythema ab igne is a dermatological condition resulting from repeated low-grade heat exposure (below the burning point), which can variably manifest with reticulated erythema and skin hyperpigmentation. Not infrequently, the cause of such a skin disorder is not immediately evident or reported by patients, especially if these are children. Compared to adults, erythema ab igne is rare in children and, if the general practitioners and pediatricians are not aware of this disorder, pediatric patients are often addressed to rheumatologists and/or undergo useless immunological investigations. Here, we performed a systematic case-based review, which finally included 32 cases of pediatric erythema ab igne (in addition to our new clinical report), and discussed the main clinical aspects and issues of this clinical entity in children. In detail, similarities of erythema ab igne with livedo reticularis and/or vasculitis-related rashes sometimes can lead to perform a panel of immunological investigations, which could be avoided. Indeed, our analysis emphasizes the importance of a careful and complete patient's anamnesis, including active questioning about the potential exposure to any physical agents (including heat sources) that may cause dermatological lesions. We also highlight some peculiarities in terms of location and heat injury in children developing erythema ab igne, based on the presence or absence of comorbidities. Conclusion: The occurrence of erythema ab igne in children (and especially in adolescents) is likely to increase in the next years because of the greater and sometimes inappropriate use of technological devices. Physicians should be aware of this condition in order to prevent patients from useless investigations, especially in the differential diagnosis of rheumatic disorders. A careful and complete patient's history with active questioning about the potential exposure to heating source is often decisive to diagnose erythema ab igne. What is Known: • Erythema ab igne is a dermatological condition which is mainly described in adults exposed to heating source at the workplace. What is New: • The occurrence of erythema ab igne in children is likely to increase in the next years because of the greater and sometimes inappropriate use of technological devices. • Erythema ab igne in children can be classified in two main categories, based on the presence or absence of comorbidity. • A careful and complete anamnesis (including the active questioning about potential exposure to any heating source) is the mainstay for diagnosing erythema ab igne in children. [ABSTRACT FROM AUTHOR]

Cytochrome c (cyt c) has been suggested as a diagnostic biomarker for non-small cell lung cancer (NSCLC) screening and is a confirmatory method for NSCLC diagnosis. In diagnosed NSCLC patients, the concentration of cyt c in the blood is decreased from the healthy range of ⁓3 nM to about ⁓1 nM. Here, by immobilizing cytochrome oxidase nanoparticles (COxNPs), onto gold nanoparticles (AuNPs) decorated graphene nanosheets (GrNs) modified pencil graphite electrode (PGE), we have constructed a high-resolution electrochemical nanosensor for the detection of the cyt c. The constructed working electrode (AuNPs-GrNs/COxNPs/PGE) was characterized by a scanning electron microscope, energy-dispersive X-ray analysis, and Fourier transform infrared spectroscopy at every stage of its construction. The proposed cyt c nanosensor performed best at optimal pH and temperature of 7.0 and 35o C, respectively, with a maximum potential of 0.317 V. Fabricated cyt c nanosensor showed a wide linear range (0.1 nM–5.1 nM) and low limit of detection (0.136 nM) with satisfactory selectivity, sensitivity (0.93mAcm−2 nM−1), and stability. The proposed approach employed less expensive raw materials to make it successful and most importantly, it is an environment-friendly method. It was successfully employed for detecting cyt c levels in sera samples of NSCLC patients and healthy individuals. [ABSTRACT FROM AUTHOR]

Phenazines are heteroaromatic compounds consisting of a central pyrazine ring fused with two benzenes. Different functional groups attached to the dibenzopyrasin core cause differences in the chemical, physical, and biological properties of phenazines. Interest in these compounds has not diminished for decades. New biological activities and practical applications discovered in recent years force researchers to investigate all aspects of the synthesis, degradation, and mechanisms of action of phenazines. In this study, we have demonstrated the involvement of the coxA gene product (cytochrome c oxidase, su I) in the production of phenazines in P. chlororaphis subsp. aurantiaca. Overlap PCR was used to knock out the coxA gene and the resulting mutants were screened for their ability to grow on rich and minimal culture media and for phenazine production. The reintroduction of the full-length coxA gene into the B-162/coxA strains was used to further confirm the role of this gene product in the ability to produce phenazines. We were able to show that the product of the coxA gene is necessary for phenazine production in rich growth media. At the same time, the CoxA protein does not seem to have any effect on phenazine production in M9 minimal salt medium. We could show that knocking down even one subunit of the cytochrome c oxidase complex leads to a significant reduction (to trace concentrations) or complete suppression of phenazine antibiotic production on rich PCA medium in P. chlororaphis subsp. aurantiaca. [ABSTRACT FROM AUTHOR]

Heme-copper respiratory oxidases are highly efficient molecular machines. These membrane enzymes catalyze the final step of cellular respiration in eukaryotes and many prokaryotes: the transfer of electrons from cytochromes or quinols to molecular oxygen and oxygen reduction to water. The free energy released in this redox reaction is converted by heme-copper respiratory oxidases into the transmembrane gradient of the electrochemical potential of hydrogen ions ΔμH+). Heme-copper respiratory oxidases have a unique mechanism for generating ΔμH+, namely, a redox-coupled proton pump. A combination of direct electrometric method for measuring the kinetics of membrane potential generation with the methods of prestationary kinetics and site-directed mutagenesis in the studies of heme-copper oxidases allows to obtain a unique information on the translocation of protons inside the proteins in real time. The review summarizes the data of studies employing time-resolved electrometry to decipher the mechanisms of functioning of these important bioenergetic enzymes. [ABSTRACT FROM AUTHOR]

In the bioenergetics studies, the direct electrometric method played an important role. This method is based on measuring the electrical potential difference (Δψ) between two compartments of the experimental cell generated by some membrane proteins. These proteins are incorporated into closed lipid–protein membrane vesicles associated with an artificial lipid membrane that separates the compartments. The very existence of such proteins able to generate Δψ was one of the consequences of Peter Mitchell's chemiosmotic concept. The discovery and investigation of their functioning contributed to the recognition of this concept and, eventually the well-deserved awarding of the Nobel Prize to P. Mitchell. Lel A. Drachev (1926-2022) was one of the main authors of the direct electrometrical method. With his participation, key studies were carried out on the electrogenesis of photosynthetic and respiratory membrane proteins, including bacteriorhodopsin, visual rhodopsin, photosynthetic bacterial reaction centers, cytochrome oxidase and others. [ABSTRACT FROM AUTHOR]

The role of protons in ATP synthase is typically considered to be energy storage in the form of an electrochemical potential, as well as an operating element proving rotation. However, this review emphasizes that protons also act as activators of conformational changes in F1 and as direct participants in phosphorylation reaction. The protons transferred through Fo do not immediately leave to the bulk aqueous phase, but instead provide for the formation of a pH gradient between acidifying Fo and alkalizing F1. It facilitates a directed inter-subunit proton transfer to F1, where they are used in the ATP synthesis reaction. This ensures that the enzyme activity is not limited by a lack of protons in the alkaline mitochondrial matrix or chloroplast stroma. Up to one hundred protons bind to the carboxyl groups of the F1 subunit, altering the electrical interactions between the amino acids of the enzyme. This removes the inhibition of ATP synthase caused by the electrostatic attraction of charged amino acids of the stator and rotor and also makes the enzyme more prone to conformational changes. Protonation occurs during ATP synthesis initiation and during phosphorylation, while deprotonation blocks the rotation inhibiting both synthesis and hydrolysis. Thus, protons participate in the functioning of all main components of ATP synthase molecular machine making it effectively a proton-driven electric machine. The review highlights the key role of protons as a coupling factor in ATP synthase with multifaceted functions, including charge and energy transport, torque generation, facilitation of conformational changes, and participation in the ATP synthesis reaction. [ABSTRACT FROM AUTHOR]

Cytochrome c oxidase (CcO) is an essential enzyme in mitochondrial and bacterial respiration. It catalyzes the four-electron reduction of molecular oxygen to water and harnesses the chemical energy to translocate four protons across biological membranes. The turnover of the CcO reaction involves an oxidative phase, in which the reduced enzyme (R) is oxidized to the metastable OH state, and a reductive phase, in which OH is reduced back to the R state. During each phase, two protons are translocated across the membrane. However, if OH is allowed to relax to the resting oxidized state (O), a redox equivalent to OH, its subsequent reduction to R is incapable of driving proton translocation. Here, with resonance Raman spectroscopy and serial femtosecond X-ray crystallography (SFX), we show that the heme a3 iron and CuB in the active site of the O state, like those in the OH state, are coordinated by a hydroxide ion and a water molecule, respectively. However, Y244, critical for the oxygen reduction chemistry, is in the neutral protonated form, which distinguishes O from OH, where Y244 is in the deprotonated tyrosinate form. These structural characteristics of O provide insights into the proton translocation mechanism of CcO. Using resonance Raman spectroscopy and serial femtosecond X-ray crystallography, the authors show the heme a3 iron and CuB in the resting oxidized form of Cytochrome c Oxidase are coordinated by a hydroxide ion and a water molecule, respectively. [ABSTRACT FROM AUTHOR]

Oral isotretinoin remains the most effective treatment for acne. The aim of this retrospective single-center cohort study was to estimate the prevalence of adverse events with the different oral isotretinoin brands used in acne treatment. The population consisted of all patients who consulted for acne between January 2015 and January 2020. The inclusion criterion was the initiation of treatment with oral isotretinoin. The exclusion criteria were the use of two or more brands during the same course of treatment and previous treatment with oral isotretinoin. Statistical analysis was carried out using Chi-square and Mann–Whitney tests. We analyzed 468 patients of whom 68.6% were female. The median age was 21 years. The median weight was 65 kg. The treatment was Roaccutane®, Curacné®, Acnotren®, Isosupra®, Contracné®, or Acnogen® in 44.2%, 28%, 14.5%, 10.5%, 1.7% and 0.4% of cases, respectively. Xerosis was the most frequently reported side effect regardless of the brand. The highest frequencies of hypercholesterolemia (25.6%) and eczema (13%) were noted with Roaccutane®; hypertriglyceridemia (16.8%), epistaxis (9.9%) and fatigue (3.1%) with Curacné®; excessive sweating (4.1%) and headache (4.1%) with Isosupra®; and abnormal liver function tests (11%) with Acnotren®. We found a significant correlation mainly between abnormal ASAT and Acnotren® (p = 0.009), hypercholesterolemia and Roaccutane® [OR = 1.652 (95% CI 1.056–2.585)], hypertriglyceridemia and higher body weight (p = 0.004). Factors related to the drug brand and to characteristics of acne patients could explain the variability in the prevalence of some adverse events. [ABSTRACT FROM AUTHOR]

Interaction between membrane proteins and ligands plays a key role in governing a wide spectrum of cellular processes. These interactions can provide a cooperative-type regulation of protein function. A wide variety of proteins, including enzymes, channels, transporters, and receptors, displays cooperative behavior in their interactions with ligands. Moreover, the ligands involved encompass a vast diversity and include specific molecules or ions that bind to specific binding sites. In this review, our particular focus is on the interaction between integral membrane proteins and ligands that can present multiple "binding sites", such as protons or membrane phospholipids. The study of the interaction that protons or lipids have with membrane proteins often presents challenges for classical mechanistic modeling approaches. In this regard, we show that, like Hill's pioneering work on hemoglobin regulation, phenomenological modeling constitutes a powerful tool for capturing essential features of these systems. [ABSTRACT FROM AUTHOR]

Kalium channelrhodopsin 1 from Hyphochytrium catenoides (HcKCR1) is a light-gated channel used for optogenetic silencing of mammalian neurons. It selects K+ over Na+ in the absence of the canonical tetrameric K+ selectivity filter found universally in voltage- and ligand-gated channels. The genome of H. catenoides also encodes a highly homologous cation channelrhodopsin (HcCCR), a Na+ channel with >100-fold larger Na+ to K+ permeability ratio. Here, we use cryo-electron microscopy to determine atomic structures of these two channels embedded in peptidiscs to elucidate structural foundations of their dramatically different cation selectivity. Together with structure-guided mutagenesis, we show that K+ versus Na+ selectivity is determined at two distinct sites on the putative ion conduction pathway: in a patch of critical residues in the intracellular segment (Leu69/Phe69, Ile73/Ser73 and Asp116) and within a cluster of aromatic residues in the extracellular segment (primarily, Trp102 and Tyr222). The two filters are on the opposite sides of the photoactive site involved in channel gating. Recently discovered kalium channelrhodopsins (KCRs) are optogenetic tools for neuronal silencing. Here, authors report cryo-electron microscopy structures of KCR1 from Hyphochytriumcatenoides and a highly homologous but sodium-selective channel from the same organism. [ABSTRACT FROM AUTHOR]

Coronavirus disease 2019 (COVID-19) infection in pediatric patients with autoimmune disorders is an area of particular concern since autoimmune diseases can increase the risk of complications from the virus. However, as the infection rates were significantly higher in adults compared to children, this at-risk group of children was relatively underrepresented in COVID-19 research. The underlying inflammatory basis of autoimmune diseases and medications that affect the immune system, such as corticosteroids, could increase the risk of severe infection in this group of patients. COVID-19 could reportedly lead to a variety of alterations in the immune system. These alterations are plausibly dependent on the underlying immune-mediated diseases or prior use of immunomodulatory drugs. Patients administrating immunomodulatory agents, especially those with severe immune system dysregulation, can experience severe symptoms of COVID-19. Nonetheless, receiving immunosuppressive medications can benefit patients by preventing cytokine storm syndromes and lung tissue damage, threatening outcomes of COVID-19. Conclusion: In this review, we sought to evaluate the currently available literature on the impact of autoimmune disease and its related therapeutic approaches on the COVID-19 infection course of disease in children and reflect on the gaps in the evidence and the need for further research in this field. What is Known: • The majority of children infected with COVID-19 demonstrate mild to moderate clinical manifestations compared to adults, whereas those children with pre-existing autoimmune conditions are at a greater risk for severe symptoms. •There is currently limited understanding of the pathophysiology and clinical outcomes of COVID-19 in pediatric patients with autoimmune disorders due to scattered reports and inadequate evidence. What is New: • Generally, children with autoimmune disorders have more unfavorable outcomes than healthy children; yet, the severity is not extreme, and is highly dependent on their autoimmune disease type and severity, as well as the medication they are taking. [ABSTRACT FROM AUTHOR]

Recombinant type III collagen plays an important role in cosmetics, wound healing, and tissue engineering. Thus, increasing its production is necessary. After an initial increase in output by modifying the signal peptide, we showed that adding 1% maltose directly to the medium increased the yield and reduced the degradation of recombinant type III collagen. We initially verified that Pichia pastoris GS115 can metabolize and utilize maltose. Interestingly, maltose metabolism–associated proteins in Pichia pastoris GS115 have not yet been identified. RNA sequencing and transmission electron microscopy were performed to clarify the specific mechanism of maltose influence. The results showed that maltose significantly improved the metabolism of methanol, thiamine, riboflavin, arginine, and proline. After adding maltose, the cell microstructures tended more toward the normal. Adding maltose also contributed to yeast homeostasis and methanol tolerance. Finally, adding maltose resulted in the downregulation of aspartic protease YPS1 and a decrease in yeast mortality, thereby slowing down recombinant type III collagen degradation. Key points: • Co-feeding of maltose improves recombinant type III collagen production. • Maltose incorporation enhances methanol metabolism and antioxidant capacity. • Maltose addition contributes to Pichia pastoris GS115 homeostasis. [ABSTRACT FROM AUTHOR]

Quinol-dependent nitric oxide reductases (qNORs) are considered members of the respiratory heme-copper oxidase superfamily, are unique to bacteria, and are commonly found in pathogenic bacteria where they play a role in combating the host immune response. qNORs are also essential enzymes in the denitrification pathway, catalysing the reduction of nitric oxide to nitrous oxide. Here, we determine a 2.2 Å cryoEM structure of qNOR from Alcaligenes xylosoxidans, an opportunistic pathogen and a denitrifying bacterium of importance in the nitrogen cycle. This high-resolution structure provides insight into electron, substrate, and proton pathways, and provides evidence that the quinol binding site not only contains the conserved His and Asp residues but also possesses a critical Arg (Arg720) observed in cytochrome bo3, a respiratory quinol oxidase. Quinol-dependent nitric oxide reductases, unique to bacteria, are considered members of respiratory heme copper oxidases. A 2.2 Å cryoEM structure of qNOR is reported shedding light on key aspects of enzyme mechanism including quinol binding and pathways for electron, substrate, and proton transport. [ABSTRACT FROM AUTHOR]

Tetrahymena thermophila, a classic ciliate model organism, has been shown to possess tubular mitochondrial cristae and highly divergent electron transport chain involving four transmembrane protein complexes (I–IV). Here we report cryo-EM structures of its ~8 MDa megacomplex IV2 + (I + III2 + II)2, as well as a ~ 10.6 MDa megacomplex (IV2 + I + III2 + II)2 at lower resolution. In megacomplex IV2 + (I + III2 + II)2, each CIV2 protomer associates one copy of supercomplex I + III2 and one copy of CII, forming a half ring-shaped architecture that adapts to the membrane curvature of mitochondrial cristae. Megacomplex (IV2 + I + III2 + II)2 defines the relative position between neighbouring half rings and maintains the proximity between CIV2 and CIII2 cytochrome c binding sites. Our findings expand the current understanding of divergence in eukaryotic electron transport chain organization and how it is related to mitochondrial morphology. Tetrahymena thermophila possesses tubular mitochondrial cristae and a highly divergent electron transport chain. Here the authors report cryo-EM structures of its half ring-shaped ~8 MDa megacomplex IV2 + (I + III2 + II)2 and ~10.6 MDa megacomplex (IV2 + I + III2 + II)2 adapted to the cristae membrane curvature. [ABSTRACT FROM AUTHOR]

Cardiolipin is a hallmark phospholipid of mitochondrial membranes. Despite established significance of cardiolipin in supporting respiratory supercomplex organization, a mechanistic understanding of this lipid-protein interaction is still lacking. To address the essential role of cardiolipin in supercomplex organization, we report cryo-EM structures of a wild type supercomplex (IV1III2IV1) and a supercomplex (III2IV1) isolated from a cardiolipin-lacking Saccharomyces cerevisiae mutant at 3.2-Å and 3.3-Å resolution, respectively, and demonstrate that phosphatidylglycerol in III2IV1 occupies similar positions as cardiolipin in IV1III2IV1. Lipid-protein interactions within these complexes differ, which conceivably underlies the reduced level of IV1III2IV1 and high levels of III2IV1 and free III2 and IV in mutant mitochondria. Here we show that anionic phospholipids interact with positive amino acids and appear to nucleate a phospholipid domain at the interface between the individual complexes, which dampen charge repulsion and further stabilize interaction, respectively, between individual complexes. Whether anionic phospholipids required for respiratory supercomplex (SC) formation is unclear. Here authors resolve SCs from a wild type and cardiolipin-deficient yeast strain at 3.2- 3.3 Å resolution to show that cardiolipin can be replaced by phosphatidylglycerol. [ABSTRACT FROM AUTHOR]

Purpose: The tarsal tunnel (TT) is a fibro-osseous anatomical space coursing from the medial ankle to the medial midfoot. This tunnel acts as a passage for both tendinous and neurovascular structures, including the neurovascular bundle containing the posterior tibial artery (PTA), posterior tibial veins (PTVs) and tibial nerve (TN). Tarsal tunnel syndrome (TTS) is the entrapment neuropathy that describes the compression and irritation of the TN within this space. Iatrogenic injury to the PTA plays a significant role in both the onset and exacerbation of TTS symptoms. The current study aims to produce a method to allow clinicians and surgeons to easily and accurately predict the bifurcation of the PTA, to avoid iatrogenic injury during treatment of TTS. Methods: Fifteen embalmed cadaveric lower limbs were dissected at the medial ankle region to expose the TT. Various measurements regarding the location of the PTA within the TT were recorded and multiple linear regression analysis performed using RStudio. Results: Analysis provided a clear correlation (p < 0.05) between the length of the foot (MH), length of hind-foot (MC) and location of bifurcation of the PTA (MB). Using these measurements, this study developed an equation (MB = 0.3*MH + 0.37*MC – 28.24 mm) to predict the location of bifurcation of the PTA within a 23° arc inferior to the medial malleolus. Conclusions: This study successfully developed a method whereby clinicians and surgeons can easily and accurately predict the bifurcation of the PTA, to avoid iatrogenic injury that would previously lead to an exacerbation of TTS symptoms. [ABSTRACT FROM AUTHOR]

Studying the effects of mechanical loads on living cells provides valuable information about their activity, vitality and intercellular communication. Mechanical stimuli have often a significant impact on cell migration, tissue remodeling and healing and other phenomena. This effects in micro scale affect also tissue structure, its mechanical characteristics and functionality. Special methods are needed to study deformation and biological responses of such small objects as cells. Moreover, in order to keep the cells alive during such tests, it is necessary to ensure appropriate environmental conditions. The methods of loading and examination cells can be categorized into several groups depending on the physical effects used in experiment. This paper provides a systematic review of the methods used in such studies and examples of mathematical modeling the mechanical response of cells to mechanical loads. Such models enable computational simulation of changes in cells and tissues excited by mechanical stress. [ABSTRACT FROM AUTHOR]

Membrane proteins are attractive targets for drug discovery due to their crucial roles in various biological processes. Studying the binding poses of amphipathic molecules to membrane proteins is essential for understanding the functions of membrane proteins and docking simulations can facilitate the screening of protein–ligand complexes at low computational costs. However, identifying docking poses for a ligand in non-aqueous environments such as lipid bilayers can be challenging. To address this issue, we propose a new docking score called logP-corrected membrane docking (LoCoMock) score. To screen putative protein–ligand complexes embedded in a membrane, the LoCoMock score considers the affinity between a target ligand and the membrane. It combines the docking score of the protein–ligand complex with the logP of the target ligand. In demonstrations using several model ligands, the LoCoMock score screened more putative complexes than the conventional docking score. As extended docking, the LoCoMock score makes it possible to screen membrane proteins more effectively as drug targets than the conventional docking. [ABSTRACT FROM AUTHOR]

Protons participate in many reactions. In proteins, protons need paths to move in and out of buried active sites. The vectorial movement of protons coupled to electron transfer reactions establishes the transmembrane electrochemical gradient used for many reactions, including ATP synthesis. Protons move through hydrogen bonded chains of waters and hydroxy side chains via the Grotthuss mechanism and by proton binding and release from acidic and basic residues. MCCE analysis shows that proteins exist in a large number of protonation states. Knowledge of the equilibrium ensemble can provide a rational basis for setting protonation states in simulations that fix them, such as molecular dynamics (MD). The proton path into the QB site in the bacterial reaction centers (RCs) of Rb. sphaeroides is analyzed by MD to provide an example of the benefits of using protonation states found by the MCCE program. A tangled web of side chains and waters link the cytoplasm to QB. MCCE analysis of snapshots from multiple trajectories shows that changing the input protonation state of a residue in MD biases the trajectory shifting the proton affinity of that residue. However, the proton affinity of some residues is more sensitive to the input structure. The proton transfer networks derived from different trajectories are quite robust. There are some changes in connectivity that are largely restricted to the specific residues whose protonation state is changed. Trajectories with QB•− are compared with earlier results obtained with QB [Wei et. al Photosynthesis Research volume 152, pages153–165 (2022)] showing only modest changes. While introducing new methods the study highlights the difficulty of establishing the connections between protein conformation. [ABSTRACT FROM AUTHOR]

From the discovery of the first membrane-interacting polymer, styrene maleic-acid (SMA), there has been a rapid development of membrane solubilising polymers. These new polymers can solubilise membranes under a wide range of conditions and produce varied sizes of nanoparticles, yet there has been a lack of broad comparison between the common polymer types and solubilising conditions. Here, we present a comparative study on the three most common commercial polymers: SMA 3:1, SMA 2:1, and DIBMA. Additionally, this work presents, for the first time, a comparative characterisation of polymethacrylate copolymer (PMA). Absorbance and dynamic light scattering measurements were used to evaluate solubilisation across key buffer conditions in a simple, adaptable assay format that looked at pH, salinity, and divalent cation concentration. Lipid-polymer nanoparticles formed from SMA variants were found to be the most susceptible to buffer effects, with nanoparticles from either zwitterionic DMPC or POPC:POPG (3:1) bilayers only forming in low to moderate salinity (< 600 mM NaCl) and above pH 6. DIBMA-lipid nanoparticles could be formed above a pH of 5 and were stable in up to 4 M NaCl. Similarly, PMA-lipid nanoparticles were stable in all NaCl concentrations tested (up to 4 M) and a broad pH range (3–10). However, for both DIBMA and PMA nanoparticles there is a severe penalty observed for bilayer solubilisation in non-optimal conditions or when using a charged membrane. Additionally, lipid fluidity of the DMPC-polymer nanoparticles was analysed through cw-EPR, showing no cooperative gel-fluid transition as would be expected for native-like lipid membranes. [ABSTRACT FROM AUTHOR]

Through their role in energy generation and regulation of several vital pathways, including apoptosis and inflammation, mitochondria are critical for the life of eukaryotic organisms. Mitochondrial dysfunction is a major problem implicated in the etiology of many pathologies, including neurodegenerative diseases, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS), diabetes, cardiovascular diseases, and many others. Proteotoxic stress, here defined as a reduction in bioenergetic activity induced by the accumulation of aberrant proteins in the mitochondria, is likely to be implicated in disease-linked mitochondrial and cellular decline. Various quality control pathways, such as mitochondrial unfolded protein response (mtUPR), the ubiquitin (Ub)-dependent degradation of aberrant mitochondrial proteins, and mitochondria-specific autophagy (mitophagy), respond to proteotoxic stress and eliminate defective proteins or dysfunctional mitochondria. This work provides a concise review of mechanisms by which disease-linked aberrant proteins affect mitochondrial function and an overview of mitochondrial quality control pathways that counteract mitochondrial proteotoxicity. We focus on mitochondrial quality control mechanisms relying on the Ub-mediated protein degradation, such as mitochondria-specific autophagy and the mitochondrial arm of the Ub proteasome system (UPS). We highlight the importance of a widening perspective of how these pathways protect mitochondria from proteotoxic stress to better understand mitochondrial proteotoxicity in overlapping pathophysiological pathways. Implications of these mechanisms in disease development are also briefly summarized. [ABSTRACT FROM AUTHOR]

The terminal oxidases of the oxidative phosphorylation pathway play a significant role in the survival and growth of M. tuberculosis, targeting these components lead to inhibition of M. tuberculosis. Many drug candidates targeting various components of the electron transport chain in M. tuberculosis have recently been discovered. The cytochrome bc1-aa3 supercomplex is one of the most important components of the electron transport chain in M. tuberculosis, and it has emerged as the novel target for several promising candidates. There are two cryo-electron microscopy structures (PDB IDs: 6ADQ and 6HWH) of the cytochrome bc1-aa3 supercomplex that aid in the development of effective and potent inhibitors for M. tuberculosis. In recent years, a number of potential candidates targeting the QcrB subunit of the cytochrome bc1 complex have been developed. In this review, we describe the recently identified inhibitors that target the electron transport chain's terminal oxidase enzyme in M. tuberculosis, specifically the QcrB subunit of the cytochrome bc1 complex. [ABSTRACT FROM AUTHOR]

Acne vulgaris (AV) is a common dermatosis that causes psychological problems. Isotretinoin is the first-line treatment for moderate-to-severe AV, but its onset of effect is delayed. Although light-based therapy is widely used in the treatment of AV, there is a lack of reports on delicate pulsed light (DPL) which has a narrow therapeutic spectrum (500-600 nm). Low-level light therapy (LLLT) has shown an emerging role in anti-inflammatory effects and skin repair. This study investigates the efficacy and safety of low-dose oral isotretinoin combined with LLLT using DPL in patients with moderate-to-severe AV. Thirty-six patients with moderate-to-severe AV were enrolled and received low-dose oral isotretinoin (10-20 mg/day). The two sides of the face were randomly assigned to receive DPL (6-9 J/cm2) or not at an interval of 2 weeks for 4 treatment sessions (weeks 0, 2, 4, 6). Photos, GAGS score, counts of papules, pustules, comedones, TEWL, melanin and erythema index, side effects, efficacy, and satisfactory score were recorded at each visit and at 4 weeks after the final treatment (week 10). Thirty-three patients completed the study. DPL and oral isotretinoin combined therapy exhibited significantly improved GAGS score as well as the number of the lesions from week 2 and maintained until week 10. At the end of the observation, the improvement of GAGS was 70.88% on the DPL and isotretinoin combined side versus 62.12% on the side with isotretinoin monotherapy (p = 0.0009). The improvement for papule number was 61.58% on the DPL combined side versus 43.33% on the control side (p < 0.0001), for comedone was 63.15% versus 43.30% (p = 0.0008). TEWL and indexes of melanin and erythema also had better outcomes with DPL combined therapy at week 10. All the side effects were temporary and tolerable; no adverse effects were observed. Oral low-dose isotretinoin combined with LLLT by DPL offers a combination with reduced side effects and better outcomes within a limited treatment duration, which advances the onset of effect of isotretinoin monotherapy and improves lesion clearance. [ABSTRACT FROM AUTHOR]

Globally, new classes of synthetic and natural antibiotics and antivirulents have continuously been validated for their potential broad-spectrum antagonistic activity with the aim of identifying an effective active molecule to prevent the spread of infectious agents in both food industry and medical field. In view of this, present study is aimed at evaluating the rapid killing efficacy of bioactive molecules Carvacrol (C) and Nerol (N) through British Standard European Norm 1276: phase2/step1 (EN1276) protocol. Active molecules C and N showed broad-spectrum antimicrobial activity against the test strains Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Enterococcus hirae at concentration range of 78.125, 625, 156.25 and 312.5 μg/mL, respectively, for C, and 625 μg/mL for N. Whereas, combinatorial approach showed efficient activity with four times reduced concentration of C and N at 78.125 and 156.25 µg/mL, respectively, against test strains. Further, EN1276 results proved the rapid killing efficacy of test strains in 1 min of contact time with significant (> 5 log) growth reduction at 100X concentration of actives. SEM analysis and reduced concentration of protease, lipids and carbohydrate contents of treated group biofilm components ascertained preformed biofilm disruption potential of C + N on polystyrene and nail surfaces. C + N at synergistic concentration exhibited no adverse effect on HaCaT cells at 78.125 µg/mL (C) + 156.25 µg/mL (N). Taken together, based on the observed experimental results, present study evidence the antiseptic/disinfectant ability of C + N and suggest that the combination can preferentially be used in foam-based hand wash formulations. [ABSTRACT FROM AUTHOR]

Treatment options for various rheumatologic diseases have been limited until the introduction of biologic agents and kinase inhibitor therapy in recent decades. Since their arrival, they have steadily been integrated into routine management. Given their wide use and overall successful outcomes, it becomes increasingly pertinent for clinicians to readily identify their side effects. Their effects can involve multiple organ systems, including hematologic. This review aims to identify and classify the range of hematologic effects associated with individual biologics and kinase inhibitors used for treatment of rheumatologic diseases. [ABSTRACT FROM AUTHOR]

Introduction: Gruber's ligament (GL), a surgical landmark, extends from the lateral upper clivus to the petrous apex (PA), forming the superior boundary of Dorello's canal (DC). It overlies the interdural segment of the abducens nerve (CN VI). High-resolution 3D skull base MRI (SB-MRI) demonstrates anatomic details visible to the surgeon, but not well seen on traditional cross-sectional imaging. The aim of this study was to demonstrate visualization of the GL and its relationship to CN VI utilizing contrast enhanced high-resolution SB-MRI. Methods: Two neuroradiologists retrospectively reviewed in consensus the SB-MRIs of 27 skull base sides, among 14 patients. GL detection rate, confidence of detection, and GL length were recorded. When GL was successfully identified, the position of the interdural segment of CN VI within DC was recorded. Results: GL was readily identified in 16 skull base sides (59%), identified with some difficulty in 2 skull base sides (7%), and failed to be identified in 9 skull base sides (33%). The mean GL length was 7.1 mm (4.5–9.3 mm). Among the 18 cases where GL was successfully identified, CN VI was readily identified in all cases (100%), coursing the lateral third of DC in 72% of sides, and middle third in the remaining 28% of sides. Conclusion: GL can be identified in approximately two-thirds of cases utilizing 3D high resolution SB-MRI. CN VI passes most commonly along the lateral third of DC. This is the first report demonstrating visualization of GL and its relation to CN VI, on imaging. [ABSTRACT FROM AUTHOR]

There is growing interest in the role of gut microbiome in colorectal cancer (CRC), ranging from screening to disease recurrence. Our study aims to identify microbial markers characteristic of CRC and to examine if changes in bacteriome persist after surgery. Forty-nine fecal samples from 25 non-cancer (NC) individuals and 12 CRC patients, before and 6-months after surgery, were collected for analysis by bacterial 16S rRNA gene sequencing. Bacterial richness and diversity were reduced, while pro-carcinogenic bacteria such as Bacteroides fragilis and Odoribacter splanchnicus were increased in CRC patients compared to NC group. These differences were no longer observed after surgery. Comparison between pre-op and post-op CRC showed increased abundance of probiotic bacteria after surgery. Concomitantly, bacteria associated with CRC progression were observed to have increased after surgery, implying persistent dysbiosis. In addition, functional pathway predictions based on the bacterial 16S rRNA gene data showed that various pathways were differentially enriched in CRC compared to NC. Microbiome signatures characteristic of CRC comprise altered bacterial composition. Elements of these dysbiotic signatures persists even after surgery, suggesting possible field-change in remnant non-diseased colon. Future studies should involve a larger sample size with microbiome data collected at multiple time points after surgery to examine if these dysbiotic patterns truly persist and also correlate with disease outcomes. [ABSTRACT FROM AUTHOR]

We succeeded in expressing selenocysteine β-lyase (SCL) from a lactic acid bacterium, Leuconostoc mesenteroides LK-151 (Lm-SCL), in the soluble fractions of Escherichia coli Rosetta (DE3) using a novel expression vector of pET21malb constructed by ourselves that has both maltose binding protein (MBP)- and 6 × His-tag. Lm-SCL acted on l-selenocysteine, l-cysteine, and l-cysteine sulfinic acid but showed a high preference for l-selenocysteine. The kcat and kcat/Km values of Lm-SCL were determined to be 108 (min−1) and 42.0 (min−1・mM−1), respectively, and this was enough catalytic efficiency to suggest that Lm-SCL might also be involved in supplying elemental selenium from l-selenocysteine to selenoproteins like other SCLs. The optimum temperature and optimum pH of Lm-SCL were determined to be 37 °C and pH 6.5, respectively. Lm-SCL was stable at 37–45 °C and pH 6.5–7.5. Lm-SCL was completely inhibited by the addition of hydroxylamine, semicarbazide, and iodoacetic acid. The enzyme activity of Lm-SCL was decreased in the presence of various metal ions, especially Cu2+. The quaternary structure of Lm-SCL is a homodimer with a subunit molecular mass of 47.5 kDa. The similarity of the primary structure of Lm-SCL to other SCLs from Citrobacter freundii, Escherichia coli, humans, or mouse was calculated to be 47.0, 48.0, 12.5, or 24.0%, respectively. Unlike Ec-SCL, our mutational and molecular docking simulation studies revealed that C362 of Lm-SCL might also catalyze the deselenation of l-selenocysteine in addition to the desulfuration of l-cysteine. [ABSTRACT FROM AUTHOR]

The function of cytochrome c oxidase as a biomolecular nanomachine that transforms energy of redox reaction into protonmotive force across a biological membrane has been subject of intense research, debate, and controversy. The structure of the enzyme has been solved for several organisms; however details of its molecular mechanism of proton pumping still remain elusive. Particularly, the identity of the proton pumping site, the key element of the mechanism, is still open to dispute. The pumping mechanism has been for a long time one of the key unsolved issues of bioenergetics and biochemistry, but with the accelerating progress in this field many important details and principles have emerged. Current advances in cytochrome oxidase research are reviewed here, along with a brief discussion of the most complete proton pumping mechanism proposed to date, and a molecular basis for control of its efficiency. [ABSTRACT FROM AUTHOR]

Abstract  The ba 3-type cytochrome c oxidase from Thermus thermophilus is phylogenetically very distant from the aa 3–type cytochrome c oxidases. Nevertheless, both types of oxidases have the same number of redox-active metal sites and the reduction of O2 to water is catalysed at a haem a 3-CuB catalytic site. The three-dimensional structure of the ba 3 oxidase reveals three possible proton-conducting pathways showing very low homology compared to those of the mitochondrial, Rhodobacter sphaeroides and Paracoccus denitrificans aa 3 oxidases. In this study we investigated the oxidative part of the catalytic cycle of the ba 3 -cytochrome c oxidase using the flow-flash method. After flash-induced dissociation of CO from the fully reduced enzyme in the presence of oxygen we observed rapid oxidation of cytochrome b (k ≅ 6.8 × 104 s−1) and formation of the peroxy (PR) intermediate. In the next step a proton was taken up from solution with a rate constant of ~1.7 × 104 s−1, associated with formation of the ferryl (F) intermediate, simultaneous with transient reduction of haem b. Finally, the enzyme was oxidized with a rate constant of ~1,100 s−1, accompanied by additional proton uptake. The total proton uptake stoichiometry in the oxidative part of the catalytic cycle was ~1.5 protons per enzyme molecule. The results support the earlier proposal that the PR and F intermediate spectra are similar (Siletsky et al. Biochim Biophys Acta 1767:138, 2007) and show that even though the architecture of the proton-conducting pathways is different in the ba 3 oxidases, the proton-uptake reactions occur over the same time scales as in the aa 3-type oxidases. [ABSTRACT FROM AUTHOR]

In aerobic organisms, cellular respiration involves electron transfer to oxygen through a series of membrane-bound protein complexes. The process maintains a transmembrane electrochemical proton gradient that is used, for example, in the synthesis of ATP. In mitochondria and many bacteria, the last enzyme complex in the electron transfer chain is cytochrome c oxidase (CytcO), which catalyses the four-electron reduction of O2 to H2O using electrons delivered by a water-soluble donor, cytochrome c. The electron transfer through CytcO, accompanied by proton uptake to form H2O drives the physical movement (pumping) of four protons across the membrane per reduced O2. So far, the molecular mechanism of such proton pumping driven by electron transfer has not been determined in any biological system. Here we show that proton pumping in CytcO is mechanistically coupled to proton transfer to O2 at the catalytic site, rather than to internal electron transfer. This scenario suggests a principle by which redox-driven proton pumps might operate and puts considerable constraints on possible molecular mechanisms by which CytcO translocates protons. [ABSTRACT FROM AUTHOR]