Light-driven Na+ pump KR2 is microbial rhodopsin found in marine bacteria in 2013. Its unique ability to actively transport Na+, but not K+, Ca2+, and H+, makes the protein a perspective tool for optogenetics – the biotechnological method for precise and minimally-invasive optical control of the living matter. The molecular mechanism of light-driven Na+ pumping has not yet been known, as the existing 3D structures of the KR2 were limited only to its inactive, ground state.
The researchers of IBS/Membrane Transporters group, with a support from ESRF, EMBL, Research Center Juelich, Moscow Institute of Physics and Technology, and ALBA synchrotron, solved the crystal structure of the pentameric (sodium pumping state) KR2 in its active, key intermediate state. The structure revealed a transient Na+ binding site inside the rhodopsin. Structure-based molecular dynamics simulations predicted Na+ pathway through the protein, which was further validated by the mutational analysis. The findings allowed the researchers to show that active light-driven Na+ transport proceeds via a combination of relay mechanism and passive diffusion of the ions through the polar cavities inside KR2.
It is shown that the mechanism of non proton cation transport is principally different from Grotthuss mechamism of proton transport in proton transporters like classical bacteriorhodopsin rhodopsin. The description of the Na+ binding site and the ion pathway in the protein facilitates the rational engineering of the enhanced KR2-based optogenetic tools.
Molecular mechanism of light-driven sodium pumping. Kovalev K, Astashkin R, Gushchin I, Orekhov P, Volkov D, Zinovev E, Marin E, Rulev M, Alekseev A, Royant A, Carpentier P, Vaganova S, Zabelskii D, Baeken C, Sergeev I, Balandin T, Bourenkov G, Carpena X, Boer R, Maliar N, Borshchevskiy V, Büldt G, Bamberg E, Gordeliy V. Nature Communications 2020, 11:2137
Contact : Valentin Gordeliy