title: Solution and crystal structures of a sugar binding site mutant of cyanovirin-N: no evidence of domain swapping.
abstract: The cyanobacterial lectin Cyanovirin-N (CV-N) exhibits antiviral activity against HIV at a low nanomolar concentration by interacting with high-mannose oligosaccharides on the virus surface envelope glycoprotein gp120. Atomic structures of wild-type CV-N revealed a monomer in solution and a domain-swapped dimer in the crystal, with the monomer comprising two independent carbohydrate binding sites that individually bind with micromolar affinity to di- and trimannoses. In the mutant CVN(mutDB), the binding site on domain B was abolished and the protein was found to be completely inactive against HIV. We determined the solution NMR and crystal structures of this variant and characterized its sugar binding properties. In solution and the crystal, CVN(mutDB) is a monomer and no domain-swapping was observed. The protein binds to Man-3 and Man-9 with similar dissociation constants ( approximately 4 muM). This confirms that the nanomolar activity of wild-type CV-N is related to the multisite nature of the protein carbohydrate interaction.
authors.affiliation: Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Matei
authors.forename: William
authors.initials: W
authors.lastname: Furey
authors.forename: Angela M
authors.initials: AM
authors.lastname: Gronenborn
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002241:Carbohydrates / Q000737:chemistry*; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D002241:Carbohydrates; D002352:Carrier Proteins; C107733:cyanovirin N