Dan Liu

Protein interactions are of paramount importance for the performance of biological functions within organisms. Post-translational modifications, including glycosylation and phosphorylation, regulate protein-protein interactions through non-covalent mechanisms. Glycosylation typically facilitates binding by altering surface properties, whereas phosphorylation can either enhance or disrupt interactions depending on context, collectively amplifying the biological impact of proteins. The entry of viruses and certain intracellular parasites into host cells is facilitated by these modifications, which permit the binding of ligands to receptors and the traversal of the cell membrane barrier. As research in this domain progresses, innovative methodologies are being developed, including protein microarrays and proximity-labeling techniques. These developments are being increasingly employed in disease prevention, therapeutics, and fundamental medical research. In light of the recent surge in emerging infectious diseases, the study of protein interactions has assumed heightened relevance. This review explores protein modifications, including glycosylation, phosphorylation, and ubiquitination, and focuses on their roles in viral entry. It highlights advanced methods for analyzing protein-protein interactions (PPIs), notably proximity labeling and protein microarrays, and concludes with novel insights into therapeutic development, aiming to inspire innovation in this evolving field.

Lactic acid bacteria (LABs) have emerged as a significant area of study within the field of probiotics due to their diverse health benefits and wide application. This review examines the various methods used to evaluate the antioxidant activity of LABs, including in vitro chemical evaluation methods, cell model evaluation methods, and in vivo evaluation methods. Comprehensive overview of the various assessment techniques employed to elucidate the multifaceted roles of LABs in enhancing the body’s natural defenses against oxidative damage. Moreover, this review emphasizes several pivotal aspects of the antioxidant effects of LABs, including the activation of the antioxidant signal pathway, the induction of antioxidative enzymes, the formation of a ROS-binding system, the production of metabolites, the enhancement of intestinal barrier integrity, the activation of the oxidative damage repair system, and the assurance of mitochondrial function. These represent the key antioxidant effects of LABs. The synthesis of this information advances our understanding of the dynamic and diverse antioxidant effects of LABs, providing a foundation for further research into their therapeutic applications in combating oxidative stress-related disorders. Future research should employ multi-omics technologies, genetic engineering, studies on synergistic effects, and large-scale clinical trials to further elucidate the molecular mechanisms underlying the antioxidant effects of LABs. This will promote their application in functional foods, pharmaceuticals, and cosmetics, providing a scientific basis for the development of more efficient antioxidant products.

Purposes: This study aimed to develop a sustainable strategy for valorizing protein-rich industrial by-products into functional antioxidants using halophilic biocatalysts, addressing environmental challenges and the demand for bioactive compounds.Methods: A moderately halophilic bacterium, Salinivibrio sp. YH4, was isolated from Yuncheng Salt Lake and identified as S. costicola (99% 16S rRNA homology). The extracellular protease EYHIII? was purified and biochemically characterized for thermal/pH stability, halotolerance, and substrate specificity. Fish collagen hydrolysates generated by EYHIII were evaluated for antioxidant capacity via 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl, and peroxyl radical scavenging assays. Cellular bioactivity was validated in high glucose-stressed human umbilical vein endothelial cells (HUVECs), analyzing ROS levels and antioxidant enzyme activity.Results: EYHIII was a thermostable (5060°C) and alkaliphilic (pH 7.59.5) M4-family metalloprotease. The enzyme retained >80% activity under high salinity conditions (1 M NaCl) and exhibited strict substrate specificity for hydrophobic residues (Phe/Leu) at the P1’ position. It efficiently hydrolyzed both soluble and insoluble collagens. Fish collagen hydrolysates generated by EYHIII demonstrated potent antioxidant activity, scavenging 33.53 ± 3.30% of DPPH radicals and 45.55 ± 3.00% of hydroxyl radicals at 3 mg/mL, with a peroxyl radical absorbance capacity of 1.69 ± 0.07 mmol TE/g. In human umbilical vein endothelial cells (HUVECs), the hydrolysate reduced high glucose-induced reactive oxygen species (ROS) to baseline levels at 200 μg/mL. It also significantly upregulated antioxidant enzymes compared to damaged controls: superoxide dismutase (SOD, 103.55%), catalase (CAT, 110.96%), and glutathione peroxidase (GSH-Px, 135.79%) (all P < 0.05).Conclusions: This study highlighted Salinivibrio sp. YH4 and its protease EYHIII as a sustainable platform for converting collagen waste into high-value antioxidants. These findings addressed both environmental pollution and the growing demand for functional bioactive compounds. The results underscored the potential of halophilic biocatalysts in advancing circular economy strategies for protein resource utilization.

Bacterial extracellular proteases from six strains of marine bacteria and seven strains of terrestrial bacteria were prepared through fermentation. Proteases were analyzed through substrate immersing zymography and used to hydrolyze the collagen and muscle proteins from a salmon skin byproduct, respectively. Collagen could be degraded much more easily than muscle protein, but it commonly showed weaker antioxidant capability. The hydrolysate of muscle proteins was prepared with crude enzymes from Pseudoalteromonas sp. SQN1 displayed the strongest activity of antioxidant in DPPH and hydroxyl radical scavenging assays (74.06% ± 1.14% and 69.71% ± 1.97%), but did not perform well in Fe²⁺ chelating assay. The antioxidant fractions were purified through ultrafiltration, cation exchange chromatography, and size exclusion chromatography gradually, and the final purified fraction U2-S2-I displayed strong activity of antioxidant in DPPH, hydroxyl radical scavenging assays (IC₅₀ = 0.263 ± 0.018 mg/mL and 0.512 ± 0.055 mg/mL), and oxygen radical absorption capability assay (1.960 ± 0.381 mmol·TE/g). The final purified fraction U2-S2-I possessed the capability to protect plasmid DNA against the damage of hydroxyl radical and its effect was similar to that of the original hydrolysis product. It indicated that U2-S2-I might be the major active fraction of the hydrolysate. This study proved that bacterial extracellular proteases could be utilized in hydrolysis of a salmon byproduct. Compared with collagen, muscle proteins was an ideal material used as an enzymatic substrate to prepare antioxidant peptides.