Formation of M-Like Intermediates in Proteorhodopsin in Alkali Solutions (pH ≥ ∼8.5) Where the Proton Release Occurs First in Contrast to the Sequence at Lower pH
| Autor: | Toshifumi Nara, Takashi Kikukawa, Jun Tamogami, Makoto Demura, Sukuna Kurokawa, Eiro Muneyuki, Seiji Miyauchi, Naoki Kamo, Keitaro Sato, Takumi Yamada |
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| Rok vydání: | 2016 |
| Předmět: |
0301 basic medicine
Halobacterium salinarum Models Molecular Aquatic Organisms Proton Lipid Bilayers Photochemistry Biochemistry 03 medical and health sciences Bacterial Proteins Rhodopsins Microbial Lipid bilayer Proteorhodopsin 030102 biochemistry & molecular biology biology Chemistry Eubacterium Bacteriorhodopsin Biological Transport Membranes Artificial Hydrogen-Ion Concentration Proton Pumps Alkali metal biology.organism_classification Photochemical Processes Recombinant Proteins Proton pump 030104 developmental biology Membrane Immobilized Proteins Amino Acid Substitution Mutation biology.protein Biocatalysis Phosphatidylcholines Algorithms Gammaproteobacteria |
| Zdroj: | Biochemistry. 55(7) |
| ISSN: | 1520-4995 |
| Popis: | Proteorhodopsin (PR) is an outward light-driven proton pump observed in marine eubacteria. Despite many structural and functional similarities to bacteriorhodopsin (BR) in archaea, which also acts as an outward proton pump, the mechanism of the photoinduced proton release and uptake is different between two H(+)-pumps. In this study, we investigated the pH dependence of the photocycle and proton transfer in PR reconstituted with the phospholipid membrane under alkaline conditions. Under these conditions, as the medium pH increased, a blue-shifted photoproduct (defined as Ma), which is different from M, with a pKa of ca. 9.2 was produced. The sequence of the photoinduced proton uptake and release during the photocycle was inverted with the increase in pH. A pKa value of ca. 9.5 was estimated for this inversion and was in good agreement with the pKa value of the formation of Ma (∼ 9.2). In addition, we measured the photoelectric current generated by PRs attached to a thin polymer film at varying pH. Interestingly, increases in the medium pH evoked bidirectional photocurrents, which may imply a possible reversal of the direction of the proton movement at alkaline pH. On the basis of these findings, a putative photocycle and proton transfer scheme in PR under alkaline pH conditions was proposed. |
| Databáze: | OpenAIRE |
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