Structural and functional characterization of fowlicidin-1, a cationic host defense peptide with potent antibacterial and LPS-neutralizing activities (52.13)

Abstract

Cathelicidins are a group of cationic host defense peptides with pluripotent immunomodulatory activities. We recently identified fowlicidin-1, a chicken cathelicidin possessing broad-spectrum antibacterial and LPS-neutralizing activities but with considerable toxicity toward mammalian cells. NMR spectroscopy revealed that fowlicidin-1 mainly adopts an α-helical conformation with glycine-induced kink in the center and a short flexible unstructured region at the N-terminal end. To reveal functional significance of different structural regions and identify peptide analog(s) with enhanced therapeutic potential, a series of deletion and substitution analogs of fowlicidin -1 were synthesized. Eight amino acids (residues 16–23) at the C-terminal end were found to be critically involved in bacterial killing, LPS binding and cytotoxicity. We also revealed that the N-terminal unstructured segment (residues 1–5) plays a minimum role in antibacterial and LPS-neutralizing activities. Removal of valine at position 5 reduced the cytotoxicity by 4-fold while retaining a similar antibacterial potency to the parent peptide. However, omission of tryptophan at position 6 resulted in at least 4-fold reduction in bacteria-killing efficiency, indicating the critical involvement of tryptophan. Taken together, fowlicidin-1(6–26) represents a short peptide analog with excellent potential to be explored as a novel antimicrobial. This project was supported by Oklahoma Center for the Advancement of Science and Technology, Oklahoma Agricultural Experiment Station and HHMI-Undergraduate Research Scholarship.