STRUCTURE OF A PROTEIN PHOTOCYCLE INTERMEDIATE BY MILLISECOND TIME-RESOLVED CRYSTALLOGRAPHY

The blue-light photoreceptor photoactive yellow protein (PYP) undergoe s a self-contained light cycle. The atomic structure of the bleached s ignaling intermediate in the light cycle of PYP was determined by mill isecond time-resolved, multiwavelength Laue crystallography and simult aneous optical spectroscopy. Light-induced trans-to-cis isomerization of the 4-hydroxycinnamyl chromophore and coupled protein rearrangement s produce a new set of active-site hydrogen bonds. An arginine gateway opens, allowing solvent exposure and protonation of the chromophore's phenolic oxygen. Resulting changes in shape, hydrogen bonding, and el ectrostatic potential at the protein surface form a likely basis for s ignal transduction. The structural results suggest a general framework for the interpretation of protein photocycles.