Antibacterial activities and conformations of synthetic α‐defensin HNP‐1 and analogs with one, two and three disulfide bridges

Abstract: Structure and biological activities of synthetic peptides corresponding to human α‐defensin HNP‐1, AC 1 YC 2 RIPAC 3 IAGERRYGTC 4 IYQGRLWAFC 5 C 6 with the S–S connectivities: C 1 –C 6 , C 2 –C 4 , C 3 –C 5 , and its variants with one, two and three disulfide bridges were investigated. Oxidation of synthetic, reduced HNP‐1 yielded a peptide with S–S connectivities C 1 –C 3 , C 2 –C 4 and C 5 –C 6 , and not with the S–S linkages as in naturally occurring HNP‐1. Selective protection of cysteine sulfhydryls was necessary for the formation of S–S bridges as in native HNP‐1. Likewise, oxidation of peptide encompassing the segment from C 2 to C 5 , resulted in the S–S linkages C 2 –C 3 and C 4 –C 5 instead of the expected linkage C 2 –C 4 and C 3 –C 5 . Antibacterial activities were observed for all peptides, irrespective of how the S–S bridges were linked. Linear peptides without S–S bridges were inactive. Circular dichroism (CD) spectra suggest that peptides constrained by one and two S–S bridges do not form rigid β‐sheet structures in an aqueous environment. The spectrum of HNP‐1 in an aqueous environment suggests the presence of a β‐hairpin conformation. In the presence of lipid vesicles, the S–S constrained peptides tend to adopt a β‐structure. Although the S–S connectivities observed in HNP‐1 may be necessary for other physiological activities, such as chemotaxis, they are clearly not essential for antibacterial activity.