NMR and calorimetric titration studies of the anti-HIV protein cyanovirin-N with branched oligomannosides: Characterization of multivalent and multi-site binding

Shenoy,S.R.; Barrientos,L.G.; Ratner,D.M.; O'Keefe,B.R.; Seeberger,P.H.; Gronenborn,A.M.; Boyd,M.R.: Chem.Biol. 9: 1109-1118, 2002.

Abstract:

Binding of the protein cyanovirin-N to oligomannose-8 and oligomannose-9 of gp120 is crucially involved in its potent virucidal activity against the human immunodeficiency virus (HIV). The interaction between cyanovirin-N and these oligosaccharides has not been thoroughly characterized due to aggregation of the oligosaccharide-protein complexes. Here, cyanovirin-N's interaction with a nonamannoside, a structural analog of oligomannose-9, has been studied by nuclear magnetic resonance and isothermal titration calorimetry. The nonamannoside interacts with cyanovirin-N in a multivalent fashion, resulting in tight complexes with an average 1:1 stoichiometry. Like the nonamannoside, an small alpha, Greek1rightwards arrow2-linked trimannoside substructure interacts with cyanovirin-N at two distinct protein subsites. The chitobiose and internal core trimannoside substructures of oligomannose-9 are not recognized by cyanovirin-N, and binding of the core hexamannoside occurs at only one of the sites on the protein. This is the first detailed analysis of a biologically relevant interaction between cyanovirin-N and high-mannose oligosaccharides of HIV-1 gp120.

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