Microbial rhodopsins are retinal-binding seven transmembrane proteins. The most well-known function of microbial rhodopsins is light-driven proton pumping and production of ATP using proton motive force, as exemplified by bacteriorhodopsins (BR), proteorhodopsins (PR), and some fungal and algal homologs. Here we report on a new type of rhodopsin, which actively and efficiently pump sodium/lithium ions. This cation-pumping rhodopsin was found from marine bacterium, where it co-exists with a PR-like proton pumping rhodopsin in the genome. In addition, we found this homolog sequences in a number of microbial species and environmental samples. This type of rhodopsin has a new proton acceptor residue instead of Asp85 (in BR). The photocycle is fast as typical pumping rhodopsins and pKa is around 5.6.  This results demonstrate that, similar to F/V-ATPases, proton-pumping rhodopsins can have sodium/lithium-pumping activities, expanding the realm of membrane bioenergetics.

New type of cation pumping microbial rhodopsins in marine bacteria

244th National Meeting (2012)

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