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The SARS-CoV-2 pandemic has continued for about three years since emerging in late December 2019, resulting in millions of deaths. Therefore, there is an urgent need to develop a safe and effective vaccine to control SARS-CoV-2. In this study, we developed a bacterium-like particle vaccine that displays the SARS-CoV-2 receptor binding domain (RBD) (named Trim-RBD-GEM) using the GEM-PA system. We evaluated the immunogenicity and protective efficacy of the Trim-RBD-GEM vaccine with the oil-in-water adjuvant AddaVax in C57BL/6 N mice intramuscularly. We found that Trim-RBD-GEM&AddaVax induced high levels of humoral immunity in C57BL/6 N mice. Additionally, the lung virus loads in the immunized group were significantly decreased compared to the adjuvant control and mock groups. Therefore, this vaccine provides protection against lethal infection in a C57BL/6 N mouse model. Our Trim-RBD-GEM&AddaVax vaccine is potentially a promising, rapid, and safe subunit vaccine for preventing and controlling SARS-CoV-2. • A bacterium-like particle vaccine in the form of SARS-CoV-2 RBD protein trimer was constructed with a purity of over 97%. • The GEM-PA surface presentation system only requires one step of centrifugation to prepare pellet antigens. • Immunization of C57BL/6 N mice with AddaVax adjuvant induced high levels of ELISA and neutralizing antibodies. • Trim-RBD-GEM using AddaVax adjuvant provided lethal protection against C57BL/6 N after the SARS-CoV-2 challenge. [ABSTRACT FROM AUTHOR]

The aim of this study was to obtain sheep bone protein hydrolysates (SBPHs) with antioxidant activity from sheep bone byproducts and evaluate their stability and processing characteristics under different conditions. Then, the antioxidant peptides were identified and synthesized, and their antioxidant mechanism of action was investigated using molecular docking. The results showed that SBPHs obtained by alkaline protease hydrolysis had high antioxidant capacity and a high proportion of hydrophobic amino acids (41.33%). The antioxidant activity of SBPHs was intolerant to high temperatures and weakly resistant to acids and alkalis. NaCl improved the reducing power, sugars maintained the antioxidant activity, and metal ions reduced the antioxidant activity of SBPHs. SBPHs maintained higher antioxidant activity after simulated gastrointestinal digestion. Three fractions were isolated by ultrafiltration, among which P–I (MW < 3 kDa) had the strongest antioxidant activity. Liquid chromatography–tandem mass spectrometry (LC‒MS/MS) showed that 17 peptides with Peptide Ranker >0.85 were found in P–I. Among the synthesized peptides, VYPFPGPIPN had the strongest antioxidant activity, which was mainly exerted through hydrogen bonding, π-π stacking and π-alkyl bonding with Keap1. This study provides a reference for subsequent studies on the production, storage and antioxidant function utilization of SBPHs. [Display omitted] • Sheep-bone protein hydrolysate had good stability and gastrointestinal tolerance. • The P–I fraction had best antioxidant activity and stability during in vitro digestion. • The peptide VN-10 displayed greater antioxidant activity than LL-5 and SN-12. • Molecular docking revealed interactions between VN-10 and Keap1. [ABSTRACT FROM AUTHOR]