Professor Sunney Xie
Department of Chemistry and Chemical Biology
Harvard University
Cambridge, Massachusetts  

Monday, November 12, 2001
3:00 pm (CT)
3269 Beckman Institute

Abstract

The single molecule approach has changed the way problems are addressed in biophysics. New insights derived from the approach are beginning to emerge. For example, we made real-time observations of enzymatic turnovers of single molecules of cholesterol oxidase, an enzyme that catalyzes the oxidation of cholesterol by oxygen [Lu et al. Science, 282, 1877 (1998)]. Statistical analyses of the data revealed a significant and slow fluctuation in the rate of cholesterol oxidation because of conformational changes. The rate fluctuation is not described by the fundamental Michaelis-Menten mechanism of enzymology, which works well for describing only the averaged behavior of turnover events. Dynamical changes of protein conformations can be either fast or slow, ranging from femtoseconds to seconds. While the fast motions can be probed by ultrafast spectroscopic techniques, the slow fluctuation, often more pertinent to chemical activity, is otherwise hidden in ensemble- averaged measurements. We have developed a new approach to study conformational dynamics on microsecond to second time scales. Measurements on single protein molecules indicate a broad distribution of conformational states and dynamical fluctuations spanning many decades of time scales. An anomalous diffusion model is able to account for the dynamical behavior. This new single-molecule approach allows probing of energy landscapes and their influence on biological functions at an unprecedented level of detail.

Tea and coffee will be served in R3151 Beckman Institute at 2:15pm.