title: A captured folding intermediate involved in dimerization and domain-swapping of GB1.
abstract: Immunoglobulin binding domain B1 of streptococcal protein G (GB1), a small (56 residues), stable, single domain protein, is one of the most extensively used model systems in the area of protein folding and design. The recently determined NMR structure of a quadruple mutant (HS#124F26A, L5V/F30V/Y33F/A34F) revealed a domain-swapped dimer that dissociated into a partially folded, monomeric species at low micromolar protein concentrations. Here, we have characterized this monomeric, partially folded species by NMR and show that extensive conformational heterogeneity for a substantial portion of the polypeptide chain exists. Exchange between the conformers within the monomer ensemble on the microsecond to millisecond timescale renders the majority of backbone amide resonances broadened beyond detection. Despite these extensive temporal and spatial fluctuations, the overall architecture of the monomeric mutant protein resembles that of wild-type GB1 and not the monomer unit of the domain-swapped dimer.
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: In-Ja L
authors.initials: IJ
authors.lastname: Byeon
authors.forename: John M
authors.initials: JM
authors.lastname: Louis
authors.forename: Angela M
authors.initials: AM
authors.lastname: Gronenborn
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus