Antimicrobial peptide CATH-1 combats Streptococcus suis by targeting the serine/threonine kinase

With the increased bacterial resistance to conventional antibiotics, there is an urgent need for the development of novel antimicrobial agents. Cathelicidins belonging to the family of cationic host defense peptides (HDPs) are a critical component of the innate immune system with antimicrobial and immunomodulatory activities. Our previous study has shown that CATH-1 exhibits potent bactericidal activity against Streptococcus suis ( S. suis ), but the underlying mechanism is still unclear. In this study, we investigated the effect of CATH-1 on the resistance development and antibacterial mechanisms against S. suis strain SC19. Our results revealed that CATH-1 did not induce bacterial drug-resistance. Proteomics and metabolomics analyses revealed that CATH-1 exerts its antibacterial effects by modulating multiple pathways, including the cell membrane, bacterial virulence, and energy metabolism pathway. Mechanistically, CATH-1 exerts dual antimicrobial effects by disrupting bacterial membrane integrity and targeting the serine/threonine kinase (STK) to inhibit capsular polysaccharide (CPS) synthesis. The interaction between STK and CATH-1 was evident by molecular docking, GST affinity-isolation assay, cellular thermal shift assay (CETSA) and drug affinity responsive target stability (DARTS). Furthermore, stk deficiency abrogated the anti- S. suis efficacy of CATH-1 both in vitro bactericidal assay and in vivo infection model, indicating that STK is the potential target of CATH-1. Our study reveals a novel antibacterial target of CATH-1, providing new insights into the development of antimicrobial peptides as anti-infective agents.