title: Role of Arg-72 of pharaonis Phoborhodopsin (sensory rhodopsin II) on its photochemistry.
abstract: Pharaonis phoborhodopsin (ppR, or pharaonis sensory rhodopsin II, NpsRII) is a sensor for the negative phototaxis of Natronomonas (Natronobacterium) pharaonis. Arginine 72 of ppR corresponds to Arg-82 of bacteriorhodopsin, which is a highly conserved residue among microbial rhodopsins. Using various Arg-72 ppR mutants, we obtained the following results: 1). Arg-72(ppR) together possibly with Asp-193 influenced the pK(a) of the counterion of the protonated Schiff base. 2). The M-rise became approximately four times faster than the wild-type. 3). Illumination causes proton uptake and release, and the pH profiles of the sequence of these two proton movements were different between R72A mutant and the wild-type; it is inferred that Arg-72 connects the proton transfer events occurring at both the Schiff base and an extracellular proton-releasing residue (Asp-193). 4). The M-decays of Arg-72 mutants were faster ( approximately 8-27 folds at pH 8 depending on mutants) than the wild-type, implying that the guanidinium prevents the proton transfer from the extracellular space to the deprotonated Schiff base. 5), The proton-pumping activities were decreased for mutants having increased M-decay rates, but the extent of the decrease was smaller than expected. The role of Arg-72 of ppR on the photochemistry was discussed.
authors.affiliation: Laboratory of Biophysical Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: Yukako
authors.initials: Y
authors.lastname: Ikeura
authors.forename: Kazumi
authors.initials: K
authors.lastname: Shimono
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iwamoto
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sudo
authors.forename: Naoki
authors.initials: N
authors.lastname: Kamo
mesh_terms: D001120:Arginine / Q000737:chemistry*; D001436:Bacteriorhodopsins / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D019791:Guanidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008027:Light; D009154:Mutation; D010713:Phosphatidylcholines / Q000737:chemistry; D010777:Photochemistry; D010782:Photolysis; D017494:Proton Pumps; D011522:Protons; D011994:Recombinant Proteins / Q000737:chemistry; D012243:Rhodopsin / Q000031:analogs & derivatives* / Q000378:metabolism*; D013997:Time Factors
chemical_list: D007477:Ions; D010713:Phosphatidylcholines; D017494:Proton Pumps; D011522:Protons; D011994:Recombinant Proteins; C045414:photorhodopsin; D002713:Chlorine; D001436:Bacteriorhodopsins; D012243:Rhodopsin; D001120:Arginine; D019791:Guanidine