Structure-activity relationship of buffalo antibacterial hepcidin analogs

Abstract

Hepcidin is an anti-microbial peptide expressed predominantly in the liver of many species. Based on the amino acid sequence deduced from buffalo (<i>Bubalus bubalis)</i> hepcidin cDNA (Accession no. EU399814), six peptides Hepc_1-25, Hepc_6-25, Hepc_7-25, Hepc_9-25, Hepc_11-25 and Hepc_15-25 were synthesized using solid-phase fluorenylmethoxycarbonyl (Fmoc) chemistry. CD spectroscopy revealed different spectra of the peptides in different solvents and in all the cases b-structure was found to be dominant with less a-helix as predicted. Quantitation of secondary structure indicated the highest b-structure for all the six peptides in SDS solution, when used as mimetic for membrane-like environment. The CD spectra of all the peptides taken in water showed that degree of randomness decreased with increase in chain length of the peptide. Out of the six peptides, only Hepc_1-25, Hepc_6-25 and Hepc_7-25 showed antibacterial activity against <i>Staphylococcus aureus </i>(Gram-positive bacteria).<i> </i>The peptides did not show any sensitivity toward <i>E. coli </i>(Gram-negative bacteria). Minimum inhibitory concentration (MIC) showed the lowest value for Hepc_7-25 as an antibacterial agent, followed by Hepc_6-25and Hepc_1-25. The peptides Hepc_9-25, Hepc_11-25and Hepc_15-25 with more random structure did not show any antimicrobial activity The study demonstrated that 5 amino acids at N-terminal in buffalo hepcidin can be truncated without loss of antimicrobial activity and further reduction of length of the analog from 20 to 19 amino acids resulted increase in the activity because of increase in <img src='/image/spc_char/beta.gif' border=0>-structure of the peptide shown by CD spectroscopy.