Watching a protein as it functions with 150-ps time-resolved X-ray crystallography

We report picosecond time-resolved x-ray diffraction from the myoglobin (Mb) mutant in which Leu(29) is replaced by Phe (L29F mutant). The frame-by-frame structural evolution, resolved to 1.8 angstroms, allows one to literally watch the protein as it executes its function. Time-resolved mid-infrared spectroscopy of flash-photolyzed L29F MbCO revealed a short-lived CO intermediate whose 140-ps lifetime is shorter than that found in wild-type protein by a factor of 1000. The electron density maps of the protein unveil transient conformational changes far more dramatic than the structural differences between the carboxy and deoxy states and depict the correlated side-chain motion responsible for rapidly sweeping CO away from its primary docking site.