title: Structural characterization of folded and unfolded states of an SH3 domain in equilibrium in aqueous buffer.
abstract: The isolated N-terminal Src homology 3 (SH3) domain of Drosophila drk exists in equilibrium between folded and unfolded states in aqueous buffer near neutral pH. Nuclear magnetic resonance spectra recorded on both states simultaneously exhibit an approximate 1:1 ratio of protein conformations. The folded form is similar to other known SH3 structures, especially the N-terminal SH3 domain of the mammalian homologue GRB2. A stretch of sequential amide-amide nuclear Overhauser effect cross-peaks for resonances of the unfolded state is observed in a region corresponding to beta-strands in the folded state. The results suggest that turn-like conformations may be preferentially sampled in the folding pathway for this predominantly beta-structured SH3 domain. In addition, a stable turn at Leu-28 is observed in the unfolded but not in the folded state. Comparison of this unfolded form with a denatured state in 2 M guanidine hydrochloride shows that, while both are highly disordered, these states are not identical and more residual structure is present under nondenaturing conditions.
authors.affiliation: Biochemistry Research Division, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: O
authors.initials: O
authors.lastname: Zhang
authors.forename: J D
authors.initials: JD
authors.lastname: Forman-Kay
mesh_terms: D000595:Amino Acid Sequence; D002021:Buffers; D029721:Drosophila Proteins; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007301:Insect Hormones / Q000737:chemistry* / Q000235:genetics; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary
chemical_list: D002021:Buffers; D029721:Drosophila Proteins; D007301:Insect Hormones; D010446:Peptide Fragments; C080530:drk protein, Drosophila