title: Real-time kinetics of electrogenic Na(+) transport by rhodopsin from the marine flavobacterium Dokdonia sp. PRO95.
abstract: Discovery of the light-driven sodium-motive pump Na(+)-rhodopsin (NaR) has initiated studies of the molecular mechanism of this novel membrane-linked energy transducer. In this paper, we investigated the photocycle of NaR from the marine flavobacterium Dokdonia sp. PRO95 and identified electrogenic and Na(+)-dependent steps of this cycle. We found that the NaR photocycle is composed of at least four steps: NaR519 + hv → K585 → (L450↔M495) → O585 → NaR519. The third step is the only step that depends on the Na(+) concentration inside right-side-out NaR-containing proteoliposomes, indicating that this step is coupled with Na(+) binding to NaR. For steps 2, 3, and 4, the values of the rate constants are 4×10(4) s(-1), 4.7 × 10(3) M(-1) s(-1), and 150 s(-1), respectively. These steps contributed 15, 15, and 70% of the total membrane electric potential (Δψ ~ 200 mV) generated by a single turnover of NaR incorporated into liposomes and attached to phospholipid-impregnated collodion film. On the basis of these observations, a mechanism of light-driven Na(+) pumping by NaR is suggested.
authors: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
authors: Alexander V
authors: AV
authors: Bogachev
authors: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
authors: Yulia V
authors: YV
authors: Bertsova
authors: Institute of Biotechnology, PO Box 65 (Viikinkaari 1) FIN-00014, University of Helsinki, Finland.
authors: Marina L
authors: ML
authors: Verkhovskaya
authors: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
authors: Mahir D
authors: MD
authors: Mamedov
authors: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
authors: Vladimir P
authors: VP
authors: Skulachev
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002414:Cations, Monovalent; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D041965:Flavobacteriaceae / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D017136:Ion Transport; D007700:Kinetics; D008027:Light; D008564:Membrane Potentials / Q000502:physiology*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D021381:Protein Transport; D011510:Proteolipids / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D002414:Cations, Monovalent; D011510:Proteolipids; D011994:Recombinant Proteins; C020485:proteoliposomes; D012243:Rhodopsin; D012964:Sodium