Features of proton transport mechanism in ESR, a retinal protein from <i>Exiguobacterium sibiricum</i>

Abstract

Retinal-containing photosensitive proteins, rhodopsins, have been detected in many microorganisms. The interest in them is largely explained by their role in storing light energy and photoregulation in microorganisms and the prospects for use in optogenetics in order to control the activity of neurons, including for the treatment of various diseases. One of the representatives of microbial rhodopsins is ESR, a retinal protein from Exiguobacterium sibiricum. The presence of a lysine residue (Lys96) as a proton donor for the Schiff base distinguishes ESR from homologous proteins. This feature, along with the hydrogen bonding of the proton acceptor Asp85 with the His57 residue, determines its functional characteristics as a proton pump. The review examines the results of ESR studies conducted using various methods, including the method of direct electrometry. Comparison of the obtained data with the results of spatial structure determination and with other retinal proteins allows drawing conclusions about the mechanisms of transport of hydrogen ions in the ESR molecule and similar retinal proteins.