Protective Role of Vitamin K3 on SARS-CoV-2 Structural Protein-Induced Inflammation and Cell Death.

The structure proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), such as nucleocapsid protein (N protein) and envelop protein (E protein), are considered to be the critical pro-inflammatory factors in coronavirus disease 2019 (COVID-19). Vitamin K3 has been reported to exert an anti-inflammatory effect. In this study, we investigated the protective effects of vitamin K3 on SARS-CoV-2 N protein induced-endothelial activation and SARS-CoV-2 E protein induced-cell death in THP-1 cells. The results showed that vitamin K3 reduced N protein-induced monocyte adhesion, suppressed the expression of adhesion molecules, and decreased the mRNA levels of pro-inflammatory cytokines in HLMECs. We confirmed that the effects of vitamin K3 on endothelial activation may be related to the inhibition of the NF-κB signal pathway. In addition, vitamin K3 reversed E protein-induced pyroptosis, inhibited NLRP3/GSDMD signal pathway and reduced the mRNA expression of pro-inflammatory cytokines in THP-1 cells. Our results also showed the protective effects of vitamin K3 on the SARS-CoV-2 structural protein-induced THP-1 cells pyroptosis and endothelial activation via NF-κB signaling pathway. These findings suggested that vitamin K3 potently suppressed the inflammatory response to prevent endothelial activation and monocyte pyroptosis induced by SARS-CoV-2 proteins. This may provide a new strategy for the treatment of COVID-19.

Integrative Strategy for Investigating the Interactions between STING and Small-Molecule Ligands.

Although small-molecule agonists of stimulator of interferon genes (STING) show significance in activating the immune system, the dynamic process involved in ligands activating STING remains unclear. Herein, we developed a biochemical strategy, integrating computer simulation and a biochemical engineering approach, to reveal the interaction mechanism between STING and 5,6-dimethylxanthenone-4-acetic acid (DMXAA), an agonist that activates the TANK binding kinase 1-interferon regulatory factor 3 signaling pathway. Specifically, inspired by an analysis of the STING-DMXAA crystal structure, we designed and synthesized DMXAA derivatives to investigate the STING-DMXAA binding model. We identified that the carboxyl moiety of DMXAA was a major pharmacophore responsive to STING activation. In particular, the loss of hydrogen bond interaction between the carboxylic acid of DMXAA and the side chain Thr262 of STING led to STING inhibition. DMXAA N-methyl amide derivative (DNHM) exhibited good inhibitor activity, inhibited STING-mediated interferon production in vitro and in vivo, and effectively attenuated STING-associated inflammatory diseases. Therefore, we provide a new insight into STING-ligand interactions, which may improve the understanding of STING biology.

Post-translational site-specific protein azidolation with an azido pyridoxal derivative.

An azido pyridoxal derivative (PLAA) was developed as a protein azidolation reagent, with selectivity towards N-terminal glycine. Successful PLAA modification was achieved with small peptides, natural proteins and lab-expressed proteins under mild conditions, offering a unique method for post-synthesis site-specific azidolation of a peptide or protein.

Bifunctional pyridoxal derivatives as efficient bioorthogonal reagents for biomacromolecule modifications.

Two types of pyridoxal analogs, azido pyridoxal (PL-N3) and carboxyl pyridoxal (PL-COOH), were developed as novel bifunctional bioorthogonal molecules. These molecules showed fast imine formation with hydrazinyl groups and stable covalent linkages via azido/carboxyl groups, and thus were of great use for site-specific peptide and protein modifications.

Fluorodibenzocyclooctynes: A Trackable Click Reagent with Enhanced Reactivity.

Bioorthogonal reactions have widespread applications in biological systems, and development of new bioorthogonal reactions has been of great interest over the past two decades. In this work, the design and synthesis of a family of fluorinated dibenzocyclooctynes (FDIBOs) are reported. The electron-deficient nature of fluorine atoms significantly accelerated the reaction of cyclooctynes in 1,3-dipolar cycloadditions, with either benzyl azide or ethyl diazoacetate, compared to conventional dibenzocyclooctyne (DIBO). In addition, FDIBOs showed unique trackable properties owing to the high NMR sensitivity of the naturally abundant 19 F isotope. Biological molecules, including a monosaccharide, a peptide, and a protein, were tested with FDIBOs, and these reactions could be easily monitored by 19 F NMR spectroscopy to evaluate the progress of the conjugation reactions. In addition, labeling of live cells was also demonstrated with metabolically modified bacteria to expand the possible applications of FDIBOs.