Characterization of the disulfide motif in BNBD-12, an antimicrobial beta-defensin peptide from bovine neutrophils.

BNBD-12, a prototype beta-defensin peptide from bovine neutrophils, was chosen for determination of the disulfide motif in this family of tridisulfide antimicrobial peptides. Disulfide-containing fragments of BNBD-12 were generated by incubation with trypsin, and the amino acid composition of one tryptic fragment allowed for the assignment of one of the three disulfides. The remaining two disulfides, contained in a 16-residue tryptic oligopeptide, were characterized by amino acid analysis of fragments generated by a single round of Edman degradation which cleaved the Cys-Cys peptide bond present near the carboxyl terminus of BNBD-12. Cleavage of this bond produced two disulfide-containing oligopeptides, the compositions of which provided unambiguous assignments of the disulfides involved. The cystine motif in BNBD-12 differs from that of classical defensins, and indicates that the beta-defensins and defensins must have differently folded chains, though they share several functional properties.