Retrocyclin-2: structural analysis of a potent anti-HIV theta-defensin.
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.
Norelle L
NL
Daly
Yi-Kuang
YK
Chen
K Johan
KJ
Rosengren
Ute C
UC
Marx
Martin L
ML
Phillips
Alan J
AJ
Waring
Wei
W
Wang
Robert I
RI
Lehrer
David J
DJ
Craik
D000595:Amino Acid Sequence; D019380:Anti-HIV Agents / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D015704:CD4 Antigens / Q000378:metabolism; D003432:Cross-Linking Reagents; D023082:Defensins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D004220:Disulfides / Q000737:chemistry; D015699:HIV Envelope Protein gp120 / Q000378:metabolism; D015497:HIV-1 / Q000187:drug effects / Q000276:immunology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding; D020836:Protein Structure, Quaternary / Q000187:drug effects; D017433:Protein Structure, Secondary; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013329:Structure-Activity Relationship
D019380:Anti-HIV Agents; D015704:CD4 Antigens; D003432:Cross-Linking Reagents; D023082:Defensins; D004220:Disulfides; D015699:HIV Envelope Protein gp120; D010456:Peptides, Cyclic; C511481:retrocyclin-2, human; C450142:theta-defensin; D012967:Sodium Dodecyl Sulfate