Control of ion balance is vital for the cells. It is controlled by membrane ion channels and pumps. The pumps usually use the energy of ATP or light. Microbial rhodopsin (MRs) light-driven ion pumps, are found in a number of microorganisms. MRs can pump various monovalent ions like Na+, K+, Cl-, I-, NO3-.
Recently found cyanobacterium Synechocystis sp. halorhodopsin (SyHR) pumps chloride. Scientists from the Membrane Transporters Group of the IBS choose the protein for the studies for three reasons. First, cyanobacteria are unusual, in opposite to other bacteria they comprise an organelle. Cl- pumps from cyanobacteria have not been studied. Second, in opposite to the most studied HRs the cyanobacterium lives in fresh water, not at high Cl- salinity. It is intriguing how the pump provides efficient ion translocation. Third, SyHR is the only characterized MR which pumps a divalent ion. It pumps sulfate (in addition to chloride). How the pump does it was a mystery.
To address these questions the authors solved the structure of SyHR in the ground, K and O intermediate states and in the sulfate-bound form. The data reveal the molecular origin of the unique properties of the protein (exceptionally strong chloride binding and proposed pumping of divalent anions) and shed light on the mechanism of anion release and uptake in cyanobacterial halorhodopsins. The unique properties of inward pumping SyHR highlight its potential as an optogenetics tool (since low concentration of Cl- is characteristic of eukaryotic cells) and may help engineer different types of anion pumps for the studies and applications.
Structural insights into light-driven anion pumping in cyanobacteria. Astashkin R, Kovalev K, Bukhdruker S, Vaganova S, Kuzmin A, Alekseev A, Balandin T, Zabelskii D, Gushchin I, Royant A, Volkov D, Bourenkov G, Koonin E, Engelhard M, Bamberg E, Gordeliy V. Nature Communications 2022 ;13:6460.
Contact : Valentin Gordeliy (IBS/Membrane Transporters Group)