title: The domain-swapped dimer of cyanovirin-N is in a metastable folded state: reconciliation of X-ray and NMR structures.
abstract: The structure of the potent HIV-inactivating protein cyanovirin-N was previously found by NMR to be a monomer in solution and a domain-swapped dimer by X-ray crystallography. Here we demonstrate that, in solution, CV-N can exist both in monomeric and in domain-swapped dimeric form. The dimer is a metastable, kinetically trapped structure at neutral pH and room temperature. Based on orientational NMR constraints, we show that the domain-swapped solution dimer is similar to structures in two different crystal forms, exhibiting solely a small reorientation around the hinge region. Mutation of the single proline residue in the hinge to glycine significantly stabilizes the protein in both its monomeric and dimeric forms. By contrast, mutation of the neighboring serine to proline results in an exclusively dimeric protein, caused by a drastic destabilization of the monomer.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Laura G
authors.initials: LG
authors.lastname: Barrientos
authors.forename: John M
authors.initials: JM
authors.lastname: Louis
authors.forename: Istvan
authors.initials: I
authors.lastname: Botos
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Mori
authors.forename: Zhaozhong
authors.initials: Z
authors.lastname: Han
authors.forename: Barry R
authors.initials: BR
authors.lastname: O'Keefe
authors.forename: Michael R
authors.initials: MR
authors.lastname: Boyd
authors.forename: Alexander
authors.initials: A
authors.lastname: Wlodawer
authors.forename: Angela M
authors.initials: AM
authors.lastname: Gronenborn
mesh_terms: D019380:Anti-HIV Agents / Q000737:chemistry; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray; D019281:Dimerization; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D019380:Anti-HIV Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D011994:Recombinant Proteins; C107733:cyanovirin N