Retrocyclin-2: structural analysis of a potent anti-HIV theta-defensinDaly, N.L., Chen, Y.K., Rosengren, K.J., Marx, U.C., Phillips, M.L., Waring, A.J., Wang, W., Lehrer, R.I., Craik, D.J.
(2007) Biochemistry 46: 9920-9928
- PubMed: 17685559
- DOI: https://doi.org/10.1021/bi700720e
- Primary Citation of Related Structures:
- PubMed Abstract:
Retrocyclins are circular mini-defensins with significant potential as agents against human immunodeficiency virus, influenza A, and herpes simplex virus. Retrocyclins bind carbohydrate-containing surface molecules such as gp120 and CD4 with high affinity (Kd, 10-100 nM), promoting their localization on cell membranes. The structural features important for activity have yet to be fully elucidated, but here, we have determined the first three-dimensional structure of a retrocyclin, namely, one of the most potent forms, retrocyclin-2. In the presence of SDS micelles, a well-defined beta-hairpin braced by three disulfide bonds that defines the cystine ladder motif is present. By contrast, a well-defined structure could not be determined in aqueous solution, suggesting that the presence of SDS micelles stabilizes the extended conformation of retrocyclin-2. Translational diffusion measurements indicate that retrocyclin-2 interacts with the SDS micelles, and such a membrane-like interaction may be an important feature in the mechanism of action of these antimicrobial peptides. Analytical ultracentrifugation and the NMR data indicated that retrocyclin-2 self-associates to form a trimer in a concentration-dependent manner. The ability to self-associate may contribute to the high-affinity binding of retrocyclins for glycoproteins by increasing the valency and enhancing the ability of retrocyclins to cross-link cell surface glycoproteins.
Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, The University of Queensland, Brisbane QLD 4072, Australia.