Synthesis, structure, and activities of an oral mucosal alpha-defensin from rhesus macaque

The oral cavity is an environment challenged by a large variety of pathogens. Consequently, the antimicrobial peptides expressed in that environment are interesting as they evolved to defend against a broad spectrum of bacteria and fungi. Here we report the discovery of new alpha-defensins from rhesus macaque oral mucosa and determine the first alpha-defensin structure from that species. The new peptides were identified by sequencing of reverse transcriptase-PCR products obtained from oral mucosal tissues, disclosing three mucosal alpha-defensins, termed rhesus macaque oral alpha-defensins (ROADs). The peptide corresponding to fully processed ROAD-1 was synthesized, subjected to folding/oxidation conditions, and purified. ROAD-1 was active against Staphylococcus aureus, Escherichia coli, and Candida albicans in a concentration-dependent manner. We determined the structure of ROAD-1 using NMR spectroscopy and find that the synthetic peptide adopts the canonical disulfide pairing and alpha-defensin fold. The antimicrobial mechanism of defensins has been correlated with their ability to disrupt and permeabilize the cell envelope, activities that depend on the surface features of the folded peptide. Although ROAD-1 maintains the defensin fold, the oral defensin displays distinct surface features when compared with other alpha-defensin structures.