title: An 15N NMR spin relaxation dispersion study of the folding of a pair of engineered mutants of apocytochrome b562.
abstract: 15N relaxation dispersion NMR spectroscopy has been used to study exchange dynamics in a pair of mutants of Rd-apocyt b562, a redesigned four-helix-bundle protein. An analysis of the relaxation data over a range of temperatures establishes that exchange in both proteins is best modeled as two-state and that it derives from the folding/unfolding transition. These results are in accord with predictions based on the reaction coordinate for the folding of the protein determined from native-state hydrogen exchange data [Chu, R.; Pei, W.; Takei, J.; Bai, Y. Biochemistry 2002, 41, 7998-8003]. The kinetics and thermodynamics of the folding transition have been characterized in detail. Although only a narrow range of temperatures could be examined, it is clear that the folding rate temperature profile is distinctly non-Arrhenius for both mutants, with the folding barrier for at least one of them entropic.
authors.affiliation: Protein Engineering Network Centers of Excellence and Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8.
authors.forename: Wing-Yiu
authors.initials: WY
authors.lastname: Choy
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zhou
authors.forename: Yawen
authors.initials: Y
authors.lastname: Bai
authors.forename: Lewis E
authors.initials: LE
authors.lastname: Kay
mesh_terms: D003198:Computer Simulation; D003573:Cytochrome b Group / Q000737:chemistry* / Q000235:genetics; D007700:Kinetics; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D015202:Protein Engineering; D017510:Protein Folding; D013816:Thermodynamics
chemical_list: D003573:Cytochrome b Group; D009587:Nitrogen Isotopes