title: Electrogenic steps of light-driven proton transport in ESR, a retinal protein from Exiguobacterium sibiricum.
abstract: A retinal protein from Exiguobacterium sibiricum (ESR) functions as a light-driven proton pump. Unlike other proton pumps, it contains Lys96 instead of a usual carboxylic residue in the internal proton donor site. Nevertheless, the reprotonation of the Schiff base occurs fast, indicating that Lys96 facilitates proton transfer from the bulk. In this study we examined kinetics of light-induced transmembrane electrical potential difference, ΔΨ, generated in proteoliposomes reconstituted with ESR. We show that total magnitude of ΔΨ is comparable to that produced by bacteriorhodopsin but its kinetic components and their pH dependence are substantially different. The results are in agreement with the earlier finding that proton uptake precedes reprotonation of the Schiff base in ESR, suggesting that Lys96 is unprotonated in the initial state and gains a proton transiently in the photocycle. The electrogenic phases and the photocycle transitions related to proton transfer from the bulk to the Schiff base are pH dependent. At neutral pH, they occur with τ 0.5ms and 4.5ms. At alkaline pH, the fast component ceases and Schiff base reprotonation slows. At pH8.4, a spectrally silent electrogenic component with τ 0.25ms is detected, which can be attributed to proton transfer from the bulk to Lys96. At pH5.1, the amplitude of ΔΨ decreases 10 fold, reflecting a decreased yield and rate of proton transfer, apparently from protonation of the acceptor (Asp85-His57 pair) in the initial state. The features of the photoelectric potential generation correlate with the ESR structure and proposed mechanism of proton transfer.
authors.affiliation: Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russian Federation. Electronic address: siletsky@genebee.msu.su.
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Siletsky
authors.affiliation: Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
authors.forename: Mahir D
authors.initials: MD
authors.lastname: Mamedov
authors.affiliation: Department of Biology, Lomonosov Moscow State University, 119234 Moscow, Leninskie gory, 1, Russian Federation.
authors.forename: Evgeniy P
authors.initials: EP
authors.lastname: Lukashev
authors.affiliation: Department of Physiology and Biophysics, University of California, Irvine 92697, USA. Electronic address: balashov@uci.edu.
authors.forename: Sergei P
authors.initials: SP
authors.lastname: Balashov
authors.affiliation: Department of Biology, Lomonosov Moscow State University, 119234 Moscow, Leninskie gory, 1, Russian Federation; Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997, Moscow, Ul. Miklukho-Maklaya, 16/10, Russian Federation.
authors.forename: Dmitriy A
authors.initials: DA
authors.lastname: Dolgikh
authors.affiliation: Department of Biology, Lomonosov Moscow State University, 119234 Moscow, Leninskie gory, 1, Russian Federation.
authors.forename: Andrei B
authors.initials: AB
authors.lastname: Rubin
authors.affiliation: Department of Biology, Lomonosov Moscow State University, 119234 Moscow, Leninskie gory, 1, Russian Federation; Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997, Moscow, Ul. Miklukho-Maklaya, 16/10, Russian Federation.
authors.forename: Mikhail P
authors.initials: MP
authors.lastname: Kirpichnikov
authors.affiliation: Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997, Moscow, Ul. Miklukho-Maklaya, 16/10, Russian Federation. Electronic address: lpetr65@yahoo.com.
authors.forename: Lada E
authors.initials: LE
authors.lastname: Petrovskaya
mesh_terms: D056449:Bacillales / Q000201:enzymology* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D008027:Light; D017494:Proton Pumps / Q000737:chemistry / Q000378:metabolism*; D011522:Protons; D012545:Schiff Bases / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D017494:Proton Pumps; D011522:Protons; D012545:Schiff Bases
keywords: Charge transfer steps; Light energy transduction; Photocycle; Photoelectric potential generation; Proton pump; Retinal protein