Figure 2From: Xenorhodopsins, an enigmatic new class of microbial rhodopsins horizontally transferred between archaea and bacteriaProtein alignment of key amino acid segments. Sequences include all xenorhodopsin homologs plus selected representatives of previously characterized microbial rhodopsin functional classes; bacteriorhodopsin (BR), halorhodopsin (HR) and sensory rhodopsins I (SR-I), II (SR-II) and III (SR-III). Shaded boxes indicate conserved residues involved in retinal binding [3]. The black box in Helix G shows a conserved Asp to Pro substitution in all xenorhodopsin proteins at this position. Retinal Schiff base proton acceptor (closed triangle) and proton donor (open triangle) residues are marked in Helix C.Back to article page