An 15N NMR spin relaxation dispersion study of the folding of a pair of engineered mutants of apocytochrome b562.
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.
Choy
Wing-Yiu
WY
Protein Engineering Network Centers of Excellence and Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8.
Zhou
Zheng
Z
Bai
Yawen
Y
Kay
Lewis E
LE
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
D003573:Cytochrome b Group; D009587:Nitrogen Isotopes