A single mutation converts bacterial Na+-transporting rhodopsin into an H+ transporter

Abstract

Na+-rhodopsins are light-driven pumps used by marine bacteria to extrude Na+ ions from the cytoplasm. We show here that replacement of Gln123 on the cytoplasmic side of the ion-conductance channel with aspartate or glutamate confers H+ transport activity to the Na+-rhodopsin from Dokdonia sp. PRO95. The Q123E variant could transport H+ out of Escherichia coli cells in a medium containing 100 mm Na+ and SCN− as the penetrating anion. The rates of the photocycle steps of this variant were only marginally dependent on Na+, and the major electrogenic steps were the decays of the K and O intermediates.