Purification, primary structures, and antibacterial activities of beta-defensins, a new family of antimicrobial peptides from bovine neutrophils

Abstract

A new family of cysteine-rich antimicrobial peptides from bovine neutrophils was isolated and characterized. Thirteen structurally homologous peptides were purified to homogeneity from a granule-rich cytoplasmic fraction of purified blood neutrophils. The complete sequences of the peptides were determined by a combination of enzymatic digestion, Edman degradation, and additional biochemical characterization of the carboxyl termini. The peptides are characterized by a highly cationic 38-42-residue chain which includes 6 invariantly spaced cysteines which form three disulfides. They share a highly conserved consensus sequence which is also found in a recently described epithelial antimicrobial peptide from bovine trachea. The in vitro antibacterial activities of the 13 neutrophil peptides, determined in assays using Staphylococcus aureus and Escherichia coli as test organisms, demonstrated that each peptide possessed antimicrobial activity, and that several were as active as the most potent neutrophil defensin, rabbit NP-1. Though the structural and functional attributes of the bovine neutrophil peptides are similar to those of defensins, the two peptide families are distinguished by their unique consensus sequences and additionally by differing tridisulfide motifs. We therefore propose that this new defensin-like antimicrobial peptide family be named beta-defensins.