FIGURE 1.

a, phylogenetic tree of microbial rhodopsins and alignment of critical amino acids of SRII- and BR-like proteins, including the two newly identified microbial rhodopsins from H. walsbyi (bopI and bopII), created using ClustalW. b, x-ray crystallographic structures of BR from H. salinarum (Protein Data Bank code 1C3W) (23) and SRII from N. pharaonis (Protein Data Bank code 1JGJ) (24), and magnified view of the critical functional site of SRII, the hydrogen bond between Tyr-174 and Thr-204.