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Publication Abstract from PubMed

The human alpha-defensins are synthesized in vivo as inactive pro-defensins, and contain a conserved glycine, Gly-17, which is part of a beta-bulge structure. It had previously been shown that the glycine main-chain torsion angles are in a D-configuration, and that D-amino acids but not L-alanine could be substituted at that position to yield correctly folded peptides without the help of a pro domain. In this study, the glycine to L-alanine mutant defensin was synthesized in the form of a pro-defensin using native chemical ligation. The ligation product folded correctly and yielded an active peptide upon CNBr cleavage. The L-Ala-17-HNP1 crystal structure depicted a beta-bulge identical to wild-type HNP1. However, dimerization was perturbed, causing one monomer to tilt with respect to the other in a dimerization model. Inhibitory activity against anthrax lethal factor (LF) showed a two-fold reduction relative to the wild-type HNP1 as measured by the inhibitory concentration IC50. Self-association was slightly reduced, as detected by surface plasmon resonance (SPR) measurements. According to the results of the virtual colony count (vCC) assay, the antibacterial activity against Escherichia coli, Staphylococcus aureus, and Bacillus cereus exhibited a less than two-fold reduction in virtual lethal dose values. Pro-defensins with two other L-amino acid substitutions, Arg and Phe, at the same position did not fold, indicating that only small side chains are tolerable. These results further elucidate the factors governing the region of the beta-bulge structure that includes Gly-17, illuminating why glycine is conserved in all mammalian alpha-defensins.

The invariant Gly residue is important for alpha defensin folding, dimerization and function: a case study of the human neutrophil alpha defensin HNP1.,Zhao L, Ericksen B, Wu X, Zhan C, Yuan W, Li X, Pazgier M, Lu W J Biol Chem. 2012 Apr 11. PMID:22496447^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.