Structure and Function of a Potent Lipopolysaccharide-Binding Antimicrobial and Anti-inflammatory Peptide

Antimicrobial peptides (AMPs) play pivotal roles in the innate defense of vertebrates. A novel AMP (cathelicidin-PY) has been identified from the skin secretions of the frog Paa yunnanensis. Cathelicidin-PY has an amino acid sequence of RKCNFLCICLICEICLRTVITSHIDKVLRPQG. Nuclear magnetic resonance (NMR) spectroscopy analysis revealed that cathelicidin-PY adopts a tertiary structure with a mostly positively charged surface containing a helix (Thr15-Ser19). It possesses strong antimicrobial activity, low hemolytic activity, low cytotoxicity against RAW 264.7 cells, and strong anti-inflammatory activity. The action of antimicrobial activity of cathelicidin-PY is through the destruction of the cell membrane. Moreover, cathelicidin-PY exerts anti-inflammatory activity by inhibiting the production of nitric oxide (NO) and inflammatory cytokines such as tumor necrosis factor (TNF-alpha), interleukin-6 (IL-6), and monocyte chemoattractant protein-1 (MCP-1). Cathelicidin-PY inhibits the activation of Toll-like receptor 4 (TLR4) inflammatory response pathways induced by lipopolysaccharide (LPS). The NMR titration experiments indicated that cathelicidin-PY can bind to LPS. In conclusion, we have identified a novel potent peptide antibiotic with both antimicrobial and anti-inflammatory activities and laid the groundwork for future research and development.