Proton Pumping Mechanism in Bacteriorhodopsin-Analysis by Infrared Spectroscopy and Site-Divected Mutagenesis.

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The Kyoto Group measured Fourier-transform infrared (FTIR) spectra of bacteriorhodopsin mutants, which were prepared by the American group, and rhodopsin upon photoreactions. The experimental plans were discussed among Kyoto, USA and Israel groups. Results obtained are summarized as follows.(1) Upon formation of the M intermediate of bacteriorhodopsin, a proton is released from Glu204. FTIR spectroscopy revealed hydrogen-bonding network between Asp85 and Glu204. A water molecule is newly found to work in the Arg82-Glu204 region.(2) FTIR spectroscopy was applied to examine hydrogen-bonding network in the Val49-Thr46-Asp96 region of the cytoplasmic side. Role of water molecules and peptide carbonyls in the structural changes in the L intermediate is revealed by use of mutants and isotope-labeled proteins.(3) FTIR spectroscopy revealed a complex of a water molecule with a chloride ion in the active center of an anion-pumping bacteriorhodopsin mutant, D85T.(4) Upon photoexcitation of rhodopsin, an intermediate called metarhodopsin-II activates transducin by specific protein-protein interaction. We invented a system to observe the spectra of the complex between metarhodopsin-II and transducin. The structural changes in the peptide backbone was detected.