Elucidation of Expression Patterns and Functional Properties of Archaerhodopsin Derived from <em>Halorubrum </em>sp. Ejinoor

Bacteriorhodopsin (BR) is a photosensitive membrane protein commonly found in Archaea, bacteria, and eukaryotes. Its biological function involves transferring protons from the cytoplasmic side to the extracellular side, converting light energy into chemical energy through ATP synthesis. Because of its simple structure and stable function, it has been widely studied in the field of optogenetics. The Halorubrum sp. Ejinoor Archaerhodopsin （HeAR）was discovered in a salt lake in Inner Mongolia, China, and shares 57% homology with BR. In this study, HeAR was expressed in E. Coli BL21(DE). Biological function of HeAR was analyzed by SDS-PAGE, UV-VIS absorption spectrum, CD spectrum, laser flash photolysis and proton pump activity detection. The results indicated that HeAR was purple and demonstrated light-dark adaptation. The maximum absorbance wavelengths for dark-adapted HeARD and light-adapted HeARL were 550 nm and 560 nm, respectively. The ratio of All-trans and 13-cis chromophore was 2:1 in HeARD and 6:1 in HeARL. The CD spectrum showed that HeAR also has trimer structure. HeAR was also a proton pump and the photochemical reaction cycle was 100 ms. Although there were L, M, N and O intermediates similar to BR in HeAR. However, the generation and disappearance time of M state is earlier than that of BR and the M state disappears before the O state. It is likely that other intermediates exist, resulting in a slow cycle. HeAR, as a photosensitive tool, may have promising applications in the field of optogenetics.