title: The point mutation A34F causes dimerization of GB1.
abstract: The immunoglobulin-binding domain B1 of streptococcal protein G (GB1), a very stable, small, single-domain protein, is one of the most extensively used models in the area of protein folding and design. Variants derived from a library of randomized hydrophobic core residues previously revealed alternative folds, namely a completely intertwined tetramer (Frank et al., Nat Struct Biol 2002;9:877-885) and a domain-swapped dimer (Byeon et al., J Mol Biol 2003;333:141-152). Here, we report the NMR structure of the single amino acid mutant Ala-34-Phe which exists as side-by-side dimer. The dimer dissociation constant is 27 +/- 4 microM. The dimer interface comprises two structural elements: First, the beta-sheets of the two monomers pair in an antiparallel arrangement, thereby forming an eight-stranded beta-sheet. Second, the alpha-helix is shortened, ending in a loop that engages in intermolecular contacts. The largest difference between the monomer unit in the A34F dimer and the monomeric wild-type GB1 is the dissolution of the C-terminal half of the alpha-helix associated with a pronounced slow conformational motion of the interface loop. This involves a large movement of the Tyr-33 side chain that swings out from the monomer to engage in dimer contacts.
authors: Department of Structural Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
authors: JunGoo
authors: J
authors: Jee
authors: In-Ja L
authors: IJ
authors: Byeon
authors: John M
authors: JM
authors: Louis
authors: Angela M
authors: AM
authors: Gronenborn
mesh_terms: D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics*; D019281:Dimerization; D008969:Molecular Sequence Data; D010649:Phenylalanine / Q000235:genetics; D017354:Point Mutation / Q000235:genetics*; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D010649:Phenylalanine; D000409:Alanine