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X‐Ray Diffraction Studies of Bacteriorhodopsin. Determination of the Positions of Mercury Label at Several Engineered Cysteine Residues
Author(s) -
Oka Toshihiko,
Kamikubo Hironari,
Tokunaga Fumio,
Lanyi Janos K.,
Needleman Richard,
Kataoka Mikio
Publication year - 1997
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1997.tb03222.x
Subject(s) - bacteriorhodopsin , mercury (programming language) , chemistry , cysteine , transmembrane protein , crystallography , diffraction , stereochemistry , membrane , biochemistry , physics , enzyme , optics , receptor , computer science , programming language
— The single cysteine‐containing bacteriorhodopsin mutants F27C, L100C, T170C, F171C and I222C were labeled with p ‐chloromercuribenzoic acid, which specifically reacts with sulfhydryl groups. These cysteines should be located at the cytoplasmic ends of the transmembrane helices A, C, F or G. We determined the positions of the bound mercury atoms by X‐ray diffraction of purple membrane films, with better than 1 Å accuracy. The determined mercury positions were compared with the structural model from cryoelectron microscopy (N. Grigorieff, T. A. Ceska, K. H. Downing, J. M. Baldwin and R. Henderson, J. Mol. Biol 259, 393‐421, 1996). Given that the distance between the mercury and the Cα atom of the cysteine in the xy plane must be shorter than 4.5 Å and that the mercury atom is located at the δ position, the positions obtained for the mercury labels agree with their expected positions from the structural model. The present results give a rationale for detecting structural changes upon illumination as shifts occur in the mercury label position.