title: Crystal structures of the HIV-1 inhibitory cyanobacterial protein MVL free and bound to Man3GlcNAc2: structural basis for specificity and high-affinity binding to the core pentasaccharide from n-linked oligomannoside.
abstract: The cyanobacterial protein MVL inhibits HIV-1 envelope-mediated cell fusion at nanomolar concentrations by binding to high mannose N-linked carbohydrate on the surface of the envelope glycoprotein gp120. Although a number of other carbohydrate-binding proteins have been shown to inhibit HIV-1 envelope-mediated cell fusion, the specificity of MVL is unique in that its minimal target comprises the Man(alpha)(1-->6)Man(beta)(1-->4)GlcNAc(beta)(1-->4)GlcNAc tetrasaccharide core of oligomannosides. We have solved the crystal structures of MVL free and bound to the pentasaccharide Man3GlcNAc2 at 1.9- and 1.8-A resolution, respectively. MVL is a homodimer stabilized by an extensive intermolecular interface between monomers. Each monomer contains two structurally homologous domains with high sequence similarity connected by a short five-amino acid residue linker. Intriguingly, a water-filled channel is observed between the two monomers. Residual dipolar coupling measurements indicate that the structure of the MVL dimer in solution is identical to that in the crystal. Man3GlcNAc2 binds to a preformed cleft at the distal end of each domain such that a total of four independent carbohydrate molecules associate with each homodimer. The binding cleft provides shape complementarity, including the presence of a deep hydrophobic hole that accommodates the N-acetyl methyl at the reducing end of the carbohydrate, and specificity arises from 7-8 intermolecular hydrogen bonds. The structures of MVL and the MVL-Man3GlcNAc2 complex further our understanding of the molecular basis of high affinity and specificity in protein-carbohydrate recognition.
authors.affiliation: Laboratory of Chemical Physics, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Williams
authors.forename: Jae Young
authors.initials: JY
authors.lastname: Lee
authors.forename: Mengli
authors.initials: M
authors.lastname: Cai
authors.forename: Carole A
authors.initials: CA
authors.lastname: Bewley
authors.forename: G Marius
authors.initials: GM
authors.lastname: Clore
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D019380:Anti-HIV Agents / Q000494:pharmacology*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000378:metabolism*; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D015699:HIV Envelope Protein gp120 / Q000737:chemistry; D006860:Hydrogen Bonding; D046911:Macromolecular Substances; D008358:Mannose / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D019380:Anti-HIV Agents; D002241:Carbohydrates; D002352:Carrier Proteins; D015699:HIV Envelope Protein gp120; D046911:Macromolecular Substances; C503888:Man(3)GlcNAc(2); D009844:Oligosaccharides; D011134:Polysaccharides; C028569:oligomannoside; D014867:Water; D008358:Mannose