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

Abstract 

Proteorhodopsin (PR), a retinal-containing seven transmembrane helix protein, functions as a light-driven proton pump. Using PCR, we isolated 18 PR variants originating from the surface of the Arctic Ocean. Their absorption maxima were between 517 and 546nm at pH 7. One of the isolates turned out to be identical to GPR (green light-absorbing proteorhodopsin) from Monterey Bay. Interestingly, 10 isolates had replaced a tyrosine in the retinal-binding site (Tyr200 in GPR) with Asn. They showed a slower photocycle, more blue-shifted absorption maxima at pH 10, and relatively larger ΔH and ΔS of activation of the transition between the O intermediate and the ground state compared to GPR.

Abbreviations: PR, proteorhodopsin, GPR, green light-absorbing proteorhodopsin, BPR, blue light-absorbing proteorhodopsin, MBP, Monterey Bay proteorhodopsin, PCR, polymerase chain reaction, DM, n-dodecyl-β-d maltopyranoside

Keywords: Proteorhodopsin, Retinal binding site, Photocycling rate, Y200N variants, Biofilm