TIME-RESOLVED LAUE CRYSTALLOGRAPHY: APPLICATION TO THE PHOTOCYCLE OF PHOTOACTIVE YELLOW PROTEIN. Zhong Ren^{[[paragraph]]}, Kingman Ng^{[[paragraph]]}, Ulrich K. Genick⁺, Gloria E. O. Borgstahl⁺, Duncan E. McRee⁺, Elizabeth D. Getzoff⁺, Claude Pradervand^{[[paragraph]]}, Wilfried Schildkamp^{[[paragraph]]} and Keith Moffat^{[[paragraph]]}, ^{[[paragraph]]}Department of Biochemistry and Molecular Biology, University of Chicago, 920 East 58th Street, Chicago, IL 60637, USA and ⁺Department of Molecular Biology, The Scripps Research Institute, 10666 North Torrey Pines Road, La Jolla, CA 92037, USA

Millisecond time-resolved Laue diffraction images obtained during the relaxation of photoactive yellow protein from its photostationary state have been analyzed. Photoactive yellow protein (PYP), a simple, water-soluble, light-sensing, bacterial photoreceptor, undergoes a reversible photocycle: blue light excites the yellow state to produce a red-shifted intermediate that relaxes to form a bleached intermediate which returns to the dark state at a rate of 2-3 s-1. Laue diffraction and simultaneous optical spectroscopy of PYP crystals during their relaxation from a photostationary state reveal the first structure of an intermediate in the photocycle of a biological macromolecule at atomic resolution. In the dark-state structure, the 4-hydroxycinnamyl chromophore (Baca et al., 1994) is buried from solvent exposure by an arginine side chain, which has been proposed to be the gateway for the phototactic signal following light excitation and the proposed trans-to-cis isomerization of the chromophore (Borgstahl et al., 1995). The time-resolved Laue diffraction patterns were analyzed by recently developed data processing algorithms, which incorporate the new concept of resolution-dependent bandpass.

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