Influence exercised by histidine-95 on chloride transport and the photocycle in halorhodopsin

The histidine residue at the 95th position (His-95) in the halorhodopsin (HR) of Halobacterium salinarium is essential for the chloride binding and pumping activity of the HR. The replacement of His-95 decreases the chloride pumping activity and formation of the intermediates of the photoreaction at low chloride levels. At physiological levels of chloride, the activity of the mutants is comparable to that of the wild-type HR. The expression and stability of the mutant HRs is less than that of the wild-type HR.