Watching a protein as it functions with picosecond X-ray crystallography and femtosecond IR spectroscopy
Abstract
Proteins are engaged in a myriad of tasks that are essential to life. To understand in mechanistic detail how proteins function, it is crucial to know the time ordering of events that give rise to their designed (or modified) function. Myoglobin (Mb), a ligand-binding heme protein, has long served as a model system for investigating ligand transport and binding in proteins. Using femtosecond time-resolved polarized IR spectroscopy, the dynamics of ligand motion after photodetachment of CO from MbCO have been probed. These studies reveal the time-dependent orientation of CO, the existence of a docking site that mediates the transport of ligands to and from the active binding site, as well as the dynamics of ligand binding and escape. To probe the structural evolution of a protein as it executes its function, a multinational collaboration has been established to acquire time-resolved X-ray crystal structures on the ID09B beam line at the European Synchrotron and Radiation Facility. Recent improvements in the experimental methodology have extended the time resolution down to 150 picoseconds and improved the spatial resolution of the electron density maps to below 2 Å. Using this technique, we have acquired time-resolved high resolution structures of L29F-MbCO, a mutant of myoglobin that exhibits unusually rapid ligand migration dynamics. The frame-by-frame structural evolution allows us to literally "watch" this protein as it functions. Conformational changes far more dramatic than the structural differences between the carboxy and deoxy states are observed. The correlated motion of CO and several side chains provides a structural explanation for the rapid expulsion of toxic CO from the nearby ligand docking site.
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2003
- Bibcode:
- 2003APS..MARB11003A