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Alzheimer’s disease (AD), a serious neurodegenerative disease, is pathologically characterized by synaptic loss and dysfunction. Synaptic vesicle protein 2A (SV2A) is an indispensable vesicular protein specifically expressed in synapses and can be used as a biomarker for synaptic density. We found that the expression of SV2A was down-regulated in the hippocampus of AD patients, yet the relation of SV2A to other hallmarks of AD pathology such as amyloid precursor protein (APP), β-amyloid (Aβ), and Tau protein is not thoroughly clear. In addition, SV2A colocalized with APP and was down-regulated at Aβ deposition. Moreover, we found that SV2A deficiency leads to a simultaneous increase in Aβ and Tau hyperphosphorylation, while SV2A overexpression was associated with downregulation of β-site APP cleaving enzyme 1 and apolipoprotein E genes. In addition, evidence gained in the study points to the phosphatidylinositol 3-kinase signaling pathway as a possible mediator in SV2A regulation influencing the incidence and development of AD. With limited effective diagnostic methods for AD, a close interplay between SV2A and AD-related proteins demonstrated in our study may provide novel and innovative diagnostic and therapeutic opportunities., Frontiers in Cell and Developmental Biology, 9, ISSN:2296-634X

Highlights • Foaming and emulsifying properties are linear correlated with glycation degree. • Ultrasound treatment enhanced glycation degree and surface properties of conjugates. • Ultrasound promoted the conversion of α-helices to β-sheets and unfolded structures. • Ultrasound induced the formation of amyloid-like fibrils of conjugates., This study aims to optimize the ultrasound treatment conditions for enhancing the degree of glycation (DG) of ovalbumin (OVA)-xylose conjugates through Maillard reaction and investigate the correlation between DG and functional properties affected by structural changes. The structural and functional properties of classical heating OVA, glycated OVA, ultrasonic treated OVA, and ultrasound-assisted glycated OVA were investigated to explore the interaction mechanism of ultrasound treatment on foaming and emulsifying properties improvement. Results indicated that the ultrasound assistance increased free sulfhydryl content, surface hydrophobicity and particle size of OVA-xylose conjugates, and thus enhancing the surface properties, which were strongly linear correlated with DG under different glycation parameters (pH, xylose/OVA ratio, heating time). Additionally, circular dichroism spectroscopy analysis revealed that ultrasound promoted the conversion of α-helices to β-sheets and unfolded structures, which was consistent with the formation of short amyloid-like aggregates that observed by atomic force microscopy phenomenon. Overall, our study provides new insights into the effects of ultrasound treatment on Maillard-induced protein functional properties enhancement, which may be a new strategy to tune the DG and functionality of protein-saccharide grafts during ultrasound processing.

Glycation can improve the functional properties of protein. However, in vitro and animal studies have shown that glycation induced lysine blockage and impaired protein digestibility. This study aimed to explore the effects of different glycation degree on the structure and digestive characteristics of ovalbumin. The results showed that glycation decreased the turbidity and hydrophobicity of the protein and changed the protein structure. Moreover, the results of in vitro simulated digestion revealed that glycation reduced the contents of essential amino acids and total amino acids after digestion. Glycation changed the amino acids and peptides release from the protein by resisting the digestion of digestive enzymes, especially trypsin. In conclusion, this work links glycation, protein digestibility, and the release of amino acids and peptides. This emphasizes the importance of the balance between improving properties and ensuring the digestibility of proteins during food processing.

This study aims to evaluate monovalent (Na+) and divalent (Mg2+) ions regulated ovalbumin (OVA) foaming properties enhancement via the change of protein structural and interfacial properties. The macro and microscopic photographs of samples after homogenization 0 min and 30 min were recorded. Results showed that foaming capacity (FC) significantly increased from 59.44 ± 16.69% to 136.67 ± 11.55% (NaCl) and 117.22 ± 5.36% (MgCl2). Accordingly, viscosity and surface intension reduced, whereas the amount of OVA adsorption increased, which suggested that ions could promote adsorption of OVA to air-water interface and further improve the foaming properties. Analogously, surface hydrophobicity (H0) increased, which revealed that the improvement of hydrophobic interactions of OVA. Besides, the β-sheet content increased, which indicated larger aggregates formed. Noteworthy, from the results of the interfacial adsorption amount and microscopic photographs, the foaming stability (FS) of samples with divalent ions was better, which could be hypothesized that protein intermolecular interactions via salt bridge may be stronger, while monovalent ions interacted with protein by nonspecific bond. Overall, our study provides a convenient approach of ions regulated structural and foaming properties of OVA, which may be a new strategy in improving the protein interfacial properties in food processing industry.

Lipid oxidation often occurs during egg white protein (EWP) storage and processing periods. Here, 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) was performed to simulate lipid oxidation to probe the oxidation effects on foaming and structural properties of EWP. Results indicated that EWP structure became unfolding and flexible after oxidation, resulting in more hydrophobic groups and negative charge exposed and soluble aggregates formed, which revealed by the results of DLS and AFM. Additionally, high resolution mass spectrometry results evidenced that ovotransferrin and lysozyme trended to be new oxidation targets with the AAPH concentration increasing, and the oxidation sites inside lysozyme proved that EWP unfolding and exposure of internal hydrophobic amino acids, which were related to the enhancement of EWP foaming properties. Overall, our study provided a further analysis of the lipid induced oxidation of EWP, which may contribute to provide a more accurate strategy for enhancing protein foaming properties in food industry.

The mechanism between food gelation and its digestibility has attracted increasing attention over the past few decades. This study aimed to evaluate the effect of glycation degree on the gelation and digestibility of egg white gel (EWG) using an in vitro model and a multi-scale characterization of gel structure. Results showed that EWG glycated with increasing d -ribose by covalent bonds exhibited better gelling properties and lower in vitro digestibility according to the appearance of soluble proteins and peptides. Besides, glycation preference for ovotransferrin at lysine might be important for regulating gel structure and proteolysis accessibility via the ratio of fibrous and granular aggregates. Moreover, gel structure was predominant over amino acids modification for digestibility. Binding disorder and steric hindrance could ascribe to the lower digestibility of gels. These findings are enlightening for the formulation and production of food matrix with controlled digestibility through glycation in food and related pharmaceutical fields.

We report the wet-state glycation of Bovine Serum Albumin (BSA) with xylose through the Maillard reaction and its effect on protein aggregations during heat treatment. Using low doses of xylose, glycation stabilized the conformations of BSA and reduced the formation of large aggregates during heat treatment. However, using high doses of xylose, glycation promoted the conversion of α-helices to unfolded structures and β-sheets, and induced the formation of short amyloid-like aggregates after heat treatment. Using high-resolution mass spectrometry, three possible glycation sites were determined on BSA treated with low dose of xylose, while six glycations sites were detected when high doses of xylose were used instead. Considering the importance of glycation to the food industry, this work not only provides new insights into the nonlinear effects of glycation on protein stability, but also provides a strategy to tune the nutritional value and functionality of proteins during food processing.

Metal ions perform a wide variety of functions associated with life processes. In this work, we investigated the influence of Mg2+ on the denaturation and aggregation of bovine serum albumin (BSA) during heat treatment. The unfolding and denaturation of proteins during food processing, especially heat treatment, has a major influence on their functional properties. Our results show that Mg2+ significantly stabilized the secondary structure of BSA when the protein was heated at 80 °C, preventing the transformation of α-helices into unfolded structures. Mg2+ also inhibited the aggregation of BSA into larger, heterogeneous structures. Moreover, after adding Mg2+, the melting temperature of BSA increased from 70.20 °C to 73.74 °C, further indicating that Mg2+ has a stabilizing effect. Finally, molecular dynamics (MD) simulations revealed that Mg2+ preferentially binds multivalently to the carboxylate groups of Asp and Glu BSA residues, and the observed stabilizing effect could be attributed to the crosslinking of secondary structure elements within BSA induced by Mg2+ binding. Considering the ubiquity of Mg2+, our work provides a facile strategy to control BSA unfolding and aggregation, which is helpful for enhancing the processing and storage properties of BSA or other proteins during food processing.