Antibasterial activities and conformations of synthetic α-defensin HNP-1 and analogs with one, two and three disulfide bridges.

Structure and biological activities of synthetic peptides corresponding to human α-defensin HNP-1, AC[sup 1]YC[sup 2]RIPAC[sup 3]IAGERRYGTC41YQGRLWAFC[sup 5]C[sup 6] with the S-S connectivities: C[sup 1]-C[su 6], C[sup 2]-C[sup 4], C[sup 3]-C[sup 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[sup 1]-C[sup 3], C[sup 2]-C[sup 4] and C[sup 5]-C[sup 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[sup 2] to C[sup 5], resulted in the S-S linkages C[sup 2]-C[sup 3] and C[sup 4]-C[sup 5] instead of the expected linkage C[sub 2]-C[sup 4] and C[sup 3]-C[sup 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 I@-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. [ABSTRACT FROM AUTHOR]