Structure‐activity relationship studies of shortened analogues of the antimicrobial peptide EeCentrocin 1 from the sea urchin Echinus esculentus

Abstract

EeCentrocin 1 is a potent antimicrobial peptide isolated from the marine sea urchin <i>Echinus esculentus</i>. The peptide has a hetero‐dimeric structure with the antimicrobial activity confined in its largest monomer, the heavy chain (HC), encompassing 30 amino acid residues. The aim of the present study was to develop a shorter drug lead peptide using the heavy chain of EeCentrocin 1 as a starting scaffold and to perform a structure‐activity relationship study with sequence modifications to optimize antimicrobial activity. The experiments consisted of 1) truncation of the heavy chain, 2) replacement of amino acids unfavourable for <i>in vitro</i> antimicrobial activity, and 3) an alanine scan experiment on the truncated and modified heavy chain sequence to identify essential residues for antimicrobial activity. The heavy chain of EeCentrocin 1 was truncated to less than half its initial size, retaining most of its original antimicrobial activity. The truncated and optimized lead peptide (<b>P6</b>) consisted of the 12 <i>N</i>‐terminal amino acid residues from the original EeCentrocin 1 HC sequence and was modified by two amino acid replacements and a <i>C</i>‐terminal amidation. Results from the alanine scan indicated that the generated lead peptide (<b>P6</b>) contained the optimal sequence for antibacterial activity, in which none of the alanine scan peptides could surpass its antimicrobial activity. The lead peptide (<b>P6</b>) was also superior in antifungal activity compared to the other peptides prepared and showed minimal inhibitory concentrations (MICs) in the low micromolar range. In addition, the lead peptide (<b>P6</b>) displayed minor haemolytic and no cytotoxic activity, making it a promising lead for further antimicrobial drug development.