Structure-function studies on bacteriorhodopsin. X. Individual substitutions of arginine residues by glutamine affect chromophore formation, photocycle, and proton translocation |
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Authors: | L J Stern H G Khorana |
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Institution: | Department of Biology, Massachusetts Institute of Technology, Cambridge 02139. |
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Abstract: | We have individually replaced all 7 of the arginine residues in bacteriorhodopsin by glutamine. The mutants with substitutions at positions 7, 164, 175, and 225 showed essentially the wild-type phenotype in regard to chromophore regeneration, chromophore lambda max, and proton pumping, although the mutant Arg-175----Gln showed decreased rate of chromophore regeneration. Glutamine substitutions of Arg-82, -134, and -227 affected proton pumping ability, and caused specific alterations in the bacteriorhodopsin photocycle. Finally, electrostatic interactions are proposed between Arg-82 and -227, and specific carboxylic acid residues in helices C and G, which regulate the purple to blue transition and proton transfers during the photocycle. |
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