Effect of Asp85 replacement by Thr on the conformation, surface electric properties and stability of bacteriorhodopsin

The role of Asp85 in maintaining bacteriorhodopsin structure has been analyzed by infrared spectroscopy, electric light scattering and differential scanning calorimetry. In comparison with the wild type bacteriorhodopsin, the mutant protein D85T shows a different conformation, electric dipole moments and decreased thermal stability. The conformational rearrangements affect both the transmembrane helices and the extramembranous protein segments. Both electric dipoles—the permanent dipole moment and the electric polarizability—have drastically lower values for the membranes containing D85T variant of bacteriorhodopsin. Therefore, this single amino acid mutation not only changes bacteriorhodopsin function, converting the protein into a halorhodopsin-like chloride pump, but it also alters its overall conformation and surface electric state.