Retinal-based anion pump from the cyanobacterium <i>Tolypothrix campylonemoides</i>

Abstract

In this work, a functional characterization of TcaR rhodopsin from the cyanobacterium Tolypothrix campylonemoides was obtained. Analysis of the amino acid sequence of TcaR revealed that this protein possesses a TSD motif that differs by only one amino acid from the motif of the known halorodopsin chloride pump TSA. The TcaR protein was expressed in E. coli, purified and incorporated into proteoliposomes and nanodiscs. Functional activity was measured by electric current generation through the planar bilayer lipid membranes (BLMs) with proteoliposomes adsorbed on one membrane surface, as well as by fluorescence using voltage-dependent dye oxonol VI. We have shown that TcaR rhodopsin functions as a powerful anion pump. Our results show that the novel microbial anion transporter TcaR deserves deeper study and may be of interest both for fundamental studies of membrane proteins and as a tool for optogenetics.