Structure determination of human and murine β‐defensins reveals structural conservation in the absence of significant sequence similarity

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Abstract
Defensins are cationic and cysteine‐rich peptides that play a crucial role in the host defense against microorganisms of many organisms by their capability to permeabilize bacterial membranes. The low sequence similarity among the members of the large mammalian β‐defensin family suggests that their antimicrobial activity is largely independent of their primary structure. To investigate to what extent these defensins share a similar fold, the structures of the two human β‐defensins, hBD‐1 and hBD‐2, as well as those of two novel murine defensins, termed mBD‐7 and mBD‐8, were determined by nuclear magnetic resonance spectroscopy. All four defensins investigated share a striking similarity on the level of secondary and tertiary structure including the lack of a distinct hydrophobic core, suggesting that the fold is mainly stabilized by the presence of three disulfide bonds. In addition to the overall shape of the molecules, the ratio of solvent‐exposed polar and hydrophobic side chains is also very similar among the four defensins investigated. It is significant that β‐defensins do not exhibit a common pattern of charged and hydrophobic residues on the protein surface and that the β‐defensin‐specific fold appears to accommodate a wide range of different amino acids at most sequence positions. In addition to the implications for the mode of biological defensin actions, these findings are of particular interest because β‐defensins have been suggested as lead compounds for the development of novel peptide antibiotics for the therapy of infectious diseases.