title: Glutamate-194 to cysteine mutation inhibits fast light-induced proton release in bacteriorhodopsin.
abstract: Substitution of glutamic acid-194, a residue on the extracellular surface of bacteriorhodopsin, with a cysteine inhibits the fast light-induced proton release that normally is coupled with the deprotonation of the Schiff base during the L to M transition. Proton release in this mutant occurs at the very end of the photocycle and coincides with deprotonation of the primary proton acceptor, Asp-85, during the O to bR transition. the E194C mutation also results in a slowing down of the photocycle by about 1 order of magnitude as compared to the wild type and produces a strong effect on the pH dependence of dark adaptation that is interpreted as a drastic reduction or elimination of the coupling between the primary proton acceptor Asp-85 and the proton release group. These data indicate that Glu-194 is a critical component of the proton release complex in bacteriorhodopsin.
authors.affiliation: Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA. sbalasho@uiuc.edu
authors.forename: S P
authors.initials: SP
authors.lastname: Balashov
authors.forename: E S
authors.initials: ES
authors.lastname: Imasheva
authors.forename: T G
authors.initials: TG
authors.lastname: Ebrey
authors.forename: N
authors.initials: N
authors.lastname: Chen
authors.forename: D R
authors.initials: DR
authors.lastname: Menick
authors.forename: R K
authors.initials: RK
authors.lastname: Crouch
mesh_terms: D001436:Bacteriorhodopsins / Q000378:metabolism*; D003545:Cysteine / Q000235:genetics*; D003623:Dark Adaptation; D018698:Glutamic Acid / Q000235:genetics*; D006217:Halobacterium; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D009154:Mutation; D011522:Protons; D013054:Spectrophotometry, Atomic
chemical_list: D011522:Protons; D018698:Glutamic Acid; D001436:Bacteriorhodopsins; D003545:Cysteine