J. Zhou, M. A. Case, J. F. Wishart and G. L. McLendon
J. Phys. Chem. B 102, 9975-9980 (1998) [Find paper at ACS Publications]
Abstract:
Transition metal ion-assembled three-helix bundle proteins provide templates to investigate the thermodynamic and dynamic structural consequences of the deletion of a single backbone hydrogen bond from an alpha-helical architecture. This deletion does not perturb the steady-state secondary structure of the protein as measured by circular dichroism spectroscopy but does decrease the overall folding free energy by ca. 0.7 kcal/mol. We have used intraprotein electron transfer as a measure of the structure-sensitive dynamics of our system. The deletion of a single hydrogen bond in one of the helices of a three-helix bundle does not significantly change the measured electron-transfer rate. This is in agreement with "Greenpath" electron-transfer pathway calculations, which assume a constant and invariant structure for the architecture. Given the exponential dependence of electron-transfer rate on distance and that fluctuations in the intervening secondary structure will cause variations in electron donor-acceptor distances, the measured electron-transfer rate associated with hydrogen bond deletion allows us to calculate a differential dynamic structural fluctuation associated with hydrogen bond deletion of less than 0.6 Å over the millisecond time scale of the experiment.