Retrocyclin, an antiretroviral theta-defensin, is a lectin.
Theta-defensins are circular octadecapeptides that contain an internal tridisulfide ladder. Because retrocyclin-1, an ancestral hominid theta-defensin, can protect human cells in vitro from infection by T- and M-tropic strains of HIV-1, we used surface plasmon resonance techniques to study its binding to glycoproteins and glycolipids implicated in HIV-1 entry. Retrocyclin-1 bound with high affinity to gp120 (K(d), 35.4 nM), CD4 (K(d), 31 nM), and galactosylceramide (K(d), 24.1 nM). Neither a circular form of retrocyclin without its tridisulfide ladder nor its beta-hairpin precursor with these disulfides intact bound gp120 or CD4 effectively. Retrocyclin also bound fetuin, an extensively glycosylated protein, with high affinity, but it did not bind nonglycosylated gp120 or BSA. However, retrocyclin did bind to a neoglycoprotein, BSA, with covalently attached sugar residues. Experiments with glycosidase-treated fetuin, gp120, and CD4 revealed that both O-linked and N-linked sugars were used as binding sites. In a panel of retrocyclin variants, binding to immobilized gp120 and CD4 were highly correlated to each other and to the peptide's ability to protect human PBMCs from infection by HIV-1. Although small, cysteine-rich antimicrobial peptides with lectin-like properties exist in plants, theta-defensins are the first such molecules to be identified in vertebrates. Retrocyclin's ability to recognize and bind carbohydrate-containing surface molecules is integrally related to its ability to protect cells from HIV-1 infection.
Wang
Wei
W
Department of Medicine, University of California, Los Angeles, CA 90095, USA.
Cole
Alexander M
AM
Hong
Teresa
T
Waring
Alan J
AJ
Lehrer
Robert I
RI
D000595:Amino Acid Sequence; D000818:Animals; D019380:Anti-HIV Agents / Q000737:chemistry* / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000378:metabolism; D015704:CD4 Antigens / Q000378:metabolism; D002236:Carbohydrate Conformation / Q000187:drug effects; D023082:Defensins / Q000737:chemistry* / Q000378:metabolism; D006031:Glycosylation; D015699:HIV Envelope Protein gp120 / Q000276:immunology / Q000378:metabolism; D015497:HIV-1 / Q000187:drug effects* / Q000276:immunology; D037102:Lectins / Q000737:chemistry* / Q000378:metabolism; D008253:Macaca mulatta; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism; D010455:Peptides; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics; D000509:alpha-Fetoproteins / Q000378:metabolism
D019380:Anti-HIV Agents; D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D023082:Defensins; D015699:HIV Envelope Protein gp120; D037102:Lectins; D009844:Oligosaccharides; D010455:Peptides; D011506:Proteins; C450143:RC 101; D000509:alpha-Fetoproteins; C450142:theta-defensin