pH Dependence of the Photoactive Yellow Protein Photocycle Investigated by Time-Resolved Crystallography.Tripathi, S., Srajer, V., Purwar, N., Henning, R., Schmidt, M.
(2012) Biophys.J. 102: 325-332
- PubMed: 22339869
- DOI: 10.1016/j.bpj.2011.11.4021
- Primary Citation of Related Structures:  3UME
- PubMed Abstract:
Visualizing the three-dimensional structures of a protein during its biological activity is key to understanding its mechanism. In general, protein structure and function are pH-dependent. Changing the pH provides new insights into the mechanisms tha ...
Visualizing the three-dimensional structures of a protein during its biological activity is key to understanding its mechanism. In general, protein structure and function are pH-dependent. Changing the pH provides new insights into the mechanisms that are involved in protein activity. Photoactive yellow protein (PYP) is a signaling protein that serves as an ideal model for time-dependent studies on light-activated proteins. Its photocycle is studied extensively under different pH conditions. However, the structures of the intermediates remain unknown until time-resolved crystallography is employed. With the newest beamline developments, a comprehensive time series of Laue data can now be collected from a single protein crystal. This allows us to vary the pH. Here we present the first structure, to our knowledge, of a short-lived protein-inhibitor complex formed in the pB state of the PYP photocycle at pH 4. A water molecule that is transiently stabilized in the chromophore active site prevents the relaxation of the chromophore back to the trans configuration. As a result, the dark-state recovery is slowed down dramatically. At pH 9, PYP stops cycling through the pB state altogether. The electrostatic environment in the chromophore-binding site is the likely reason for this altered kinetics at different pH values.
University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA.