Spectroscopic and photochemical analysis of proteorhodopsin variants from the surface of the Arctic Ocean

Abstract

Proteorhodopsin (PR), a retinal-containing seven transmembrane protein that functions as a light-driven proton pump, was discovered in the genome of marine bacteria. Eighteen PRs were isolated using PCR from the surface of the Arctic Ocean. Interestingly, there are several isolates in which the retinal binding site member Tyr200 (in MBP) is replaced with Asn. They show a slow photocycle and more blue shifted absorption maxima than GPR at pH 10. Y200N variant shows larger ？H than in GPR, and we suggest that they have been adapted to environmental temperature changes by modulating its photocycling rate.