Catestatin (bCGA(344-364)), an endogenous peptide of bovine chromogranin A, was initially characterized for its effect on the inhibition of catecholamine release from chromaffin cells. Catestatin and its active domain (bCGA(344-358)) were identified in chromaffin cells and in secretion medium. The present study identified a potent antimicrobial activity of bCGA(344-358) in the lowmicromolar range against bacteria, fungi and yeasts, without showing any haemolytic activity. Confocal laser microscopy demonstrated penetration of the rhodaminated peptide into the cell membranes of fungi and yeasts and its intracellular accumulation. Time-lapse videomicroscopy showed arrest of fungal growth upon penetration of the labelled peptide into a fungal filament. We identified several catestatin-containing fragments in the stimulated secretion medium of human polymorphonuclear neutrophils, suggesting the N-terminal sequence of catestatin (bCGA(344-358)) (named cateslytin) as a novel component of innate immunity.

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Effects of salicylic acid (SA) on gibberellin (GA) homeostasis, C-repeat/dehydration-responsive element binding factor (CBF) pathway, and antioxidant enzyme systems linked to chilling- and oxidative-stress tolerance in tomato fruit were investigated. Mature green tomatoes (Solanum lycopersicum L. cv. Moneymaker) were treated with 0, 0.5, and 1 mM SA solution for 15 min before storage at 4 °C for 28 days. In comparison to 0 or 0.5 mM SA, 1 mM SA significantly decreased the chilling injury (CI) index in tomato fruit. In the SA-treated fruit, the upregulation of GA biosynthetic gene (GA3ox1) expression was followed by gibberellic acid (GA) surge and DELLA protein degradation. CBF1 participated in the SA-modulated tolerance and stimulated the expression of GA catabolic gene (GA2ox1). Furthermore, 1 mM SA enhanced activities of antioxidant enzymes and, thus, reduced reactive oxygen species accumulation. Our findings suggest that SA might protect tomato fruit from CI and oxidative damage through regulating GA metabolism, CBF1 gene expression, and antioxidant enzyme activities.

Food-derived hypotensive peptides have attracted attention in the field of active peptide research in recent years. In this study, based on ACE inhibition rate and using the Box–Behnken central combination design principle to optimise the process of ACE inhibitor peptides prepared by double-enzyme hydrolysis. The amino acid sequences of ACE inhibitor peptides were determined by liquid chromatography mass spectrometry (LC-MS/MS), and their binding to ACE was studied by molecular docking. The optimal processing conditions were 1:1 alkaline protease: compound protease, pH was 8.43, enzymolysis temperature was 44.32 °C, and enzymolysis time was 3.52 h. Under these conditions, the ACE inhibition rate reached 65.12%, and the inhibition rate after separation and purification was 80.68% (IC50 = 0.9 mg/mL). Three novel peptides with ACE inhibitory activity were detected by LC-MS/MS, with sequences LVYP (Leu-Val-Tyr-Pro), VYPW(Val-Tyr-Pro-Trp) and YPWT(Tyr-Pro-Trp-Thr). Molecular docking revealed that the three novel peptides all established hydrogen bonds with the S1(Tyr523, Glu384, Ala354) and S2 (His353) pockets of ACE. Among them, LVYP, VYPW and YPWT, respectively, formed eleven hydrogen bonds, six hydrogen bonds and nine hydrogen bonds with ACE. The study revealed that these peptides have the potential for the development of novel ACE inhibitor drugs and provide a new avenue for high-value utilisation of mushrooms scraps.

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