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

OBJECTIVES

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.

PURPOSE: This study investigated the effect of CATH-1 on the resistance development and antibacterial mechanisms against S. suis.

METHODS

Drug resistance induction assays, time-kill curves, and Live/Dead bacterial staining were used in this study. To analyze the potential antibacterial targets of CATH-1, integrated proteomic and metabolomic analysis, scanning and transmission electron microscopy, membrane potential determination, molecular docking, GST affinity-isolation assay, cellular thermal shift assay (CETSA), and drug affinity responsive target stability assays (DARTS) were employed. Furthermore, the crucial role of STK in the antibacterial activity of CATH-1 was validated through both in vitro bactericidal tests and a mouse infection model.

RESULTS

CATH-1 did not readily induce resistance in S. suis. Multi-omics analysis revealed that CATH-1 exerts its antibacterial effects by modulating multiple pathways, including those related to the cell membrane, bacterial virulence, and energy metabolism. Mechanistically, CATH-1 exhibits dual antibacterial actions by disrupting bacterial membrane integrity and targeting the STK pathway to inhibit capsular polysaccharide (CPS) synthesis. Direct binding between CATH-1 and STK was confirmed by CETSA and DARTS. Crucially, the deletion of the stk gene significantly attenuated the anti-infective efficacy of CATH-1 both in vitro and in vivo.

CONCLUSION

This study reveals a novel dual anti-bacterial mechanism of action of CATH-1, inclduing membrane disruption and inhibition of STK-mediated CPS synthesis, and identifies STK as its key functional target. These findings provide a crucial theoretical foundation and new directions for developing novel anti-infective strategies based on antimicrobial peptides.