Light-driven proton pump that generates photothrophic energy. Contains one covalently linked retinal chromophore. It presents a fast proton release and an alkaliphilic photocycle, consistent with its marine origin and the near-surface environment where this bacterium was collected. Transport occurs only at pHs above 7 and is unidirectional. Mutagenesis experiments that removed all the Cys residues of GPR show that at least one of the Cys residues in the protein is probably modified post-translationally. Belongs to the archaeal/bacterial/fungal opsin family.