Bacteriorhodopsin
Bacteriorhodopsin is a photosynthetic pigment used by archaea, most notably halobacteria. An integral membrane protein, it belongs to the "7TM receptor family," so-called because each is composed of seven transmembrane alpha helices. The amino acid sequences of the bacteriorhodopsins resemble those of vertebrate rhodopsins, which are the pigments that sense light in the retina. Evidence from crystallography confirms that the two classes of proteins are also similar in shape or tertiary structure.
