REVIEW: Features of the Mechanism of Proton Transport in ESR, Retinal Protein from Exiguobacterium sibiricum

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Lada E. Petrovskaya^1,a*, Sergei A. Siletsky², Mahir D. Mamedov², Eugene P. Lukashev³, Sergei P. Balashov⁴, Dmitry A. Dolgikh^1,3, and Mikhail P. Kirpichnikov^1,3

¹Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia

²Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia

³Faculty of Biology, Lomonosov Moscow State University, 119234 Moscow, Russia

⁴Department of Physiology and Biophysics, University of California, 92697 Irvine CA

^* To whom correspondence should be addressed.

Received June 6, 2023; Revised July 11, 2023; Accepted July 11, 2023

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Retinal-containing light-sensitive proteins – rhodopsins – are found in many microorganisms. Interest in them is largely explained by their role in light energy storage and photoregulation in microorganisms, as well as the prospects for their use in optogenetics to control neuronal activity, including treatment of various diseases. One of the representatives of microbial rhodopsins is ESR, the retinal protein of Exiguobacterium sibiricum. What distinguishes ESR from homologous proteins is the presence of a lysine residue (Lys96) as a proton donor for the Schiff base. This feature, along with the hydrogen bond of the proton acceptor Asp85 with the His57 residue, determines functional characteristics of ESR as a proton pump. This review examines the results of ESR studies conducted using various methods, including direct electrometry. Comparison of the obtained data with the results of structural studies and with other retinal proteins allows us to draw conclusions about the mechanisms of transport of hydrogen ions in ESR and similar retinal proteins.

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KEY WORDS: retinal protein, proteorhodopsin, Schiff base, proton acceptor, proton donor, photocycle, direct electrometric method

DOI: 10.1134/S0006297923100103

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