Isolation of a gene that encodes a new retinal protein, archaerhodopsin, from Halobacterium sp. aus-1

We have cloned and sequenced the gene that encodes archaerhodopsin, a light-driven H+ pump in Halobacterium sp. aus-1 (Mukohata, Y., Sugiyama, Y., Ihara, K., and Yoshida, M. (1988) Biochem. Biophys. Res. Commun. 151, 1339-1345). The nucleotide sequence of this gene contained an open reading frame which corresponded to a protein of 260 amino acids with a molecular mass of 27,851 daltons, including a precursor sequence of 6 amino acids at the amino terminus and 2 amino acids at the carboxyl terminus. The deduced amino acid sequence of archaerhodopsin exhibited 59 and 32% homology to the sequences of bacteriorhodopsin and halorhodopsin, respectively, from Halobacterium halobium. Three charged residues (Asp-121, Asp-218, and Lys-222) are conserved in the transmembrane segments among the three retinal proteins. Residues Asp-91 and Asp-102 which, it has been suggested, may be essential for the pumping of protons (Mogi, T., Stern, L. J., Marti, T., Chao, B. H., and Khorana, H. G. (1988) Proc. Natl. Acad. Sci. U. S. A. 85,4148-4152) are conserved between archaerhodopsin and bacteriorhodopsin.