Design of non-toxic analogs of cathelicidin-derived bovine anti-microbial peptide BMAP–27: The role of leucine as well as phenylalanine zipper sequences in determining its toxicity

Abstract

BMAP-27 is a cathelicidin-derived bovine anti-microbial peptide, which shows moderate cytotoxicity and potent antibacterial activity against a wide variety of microorganisms. Despite a number of studies, very little is known about the amino acid sequences of this peptide that controls its antibacterial and cytotoxic activities. A small stretches of phenylalanine and leucine zipper sequences were identified at the N- and C-terminals of the molecule respectively. In order to understand the structural and functional roles of these sequence elements several analogs of BMAP-27 were synthesized and characterized after substituting leucine/phenylalanine residue(s) at ‘a’ and/or ‘d’ positions of the leucine and phenylalanine zipper sequences respectively by alanine. The BMAP-27 analogs exhibited significantly reduced cytotoxicity against the human red blood (hRBC) and murine 3T3 cells as compared to that of the wild type peptide. Interestingly, BMAP-27 and its analogs exhibited comparable antibacterial activity against the selected Gram (+)ve and (-)ve bacteria. Moreover, BMAP-27 and its analogs showed similar localization, assembly onto the selected bacteria and induced comparable permeability in these cells. However, only BMAP-27 but not its analogs assembled and bound strongly onto the hRBCs and permeabilized them. The results indicated that not only a leucine zipper but also a phenylalanine zipper sequence plays an important role in maintaining the assembly of BMAP-27 onto the mammalian cells examined here and cytotoxic activity against them. To our knowledge this is the first report on the evaluation of structural and functional roles of a phenylalanine zipper sequence in a naturally occurring antimicrobial peptide.