Salt bridge in the conserved His-Asp cluster in Gloeobacter rhodopsin contributes to trimer formation

Gloeobacter rhodopsin (GR) is a eubacterial proton pump having a highly conserved histidine near the retinal Schiff base counter-ion, aspartate. Various interactions between His and Asp of the eubacterial proton pump have been reported. Here, we showed the pH-dependent trimer/monomer transition of GR in the presence of dodecyl-β-d-maltoside by size-exclusion chromatography. The pH dependence was closely related to the protonation state of the counter-ion, Asp121. For the H87M mutant, pH dependence disappeared and a monomer became dominant. We concluded that the formation or breaking of the salt bridge between His87 and Asp121 inside the protein changes the quaternary structure.Structured summary of protein interactionsRhodopsin and Rhodopsin bind by molecular sieving (View interaction)Rhodopsin and Rhodopsin bind by molecular sieving (View interaction: 1, 2)