The bacteriochlorophyll a-binding polypeptide B806–866-β was extracted from membranes of the green thermophilic bacterium Chloroflexus aurantiacus with chloroform/methanol/ammonium acetate. Purification of the antenna polypeptide (6.3 kDa) was achieved by chromatography on Sephadex LH-60, Whatman DE-32 and by FPLC. The complete amino acid sequence (53 amino acid residues) was determined. The B806–866-β polypeptide is sequence homologous to the antenna β-polypeptides of purple bacteria (27–40%) and exhibits the characteristic three domain structure of the B870, B800–850 and B800–820 antenna complexes. The two typical His residues, conserved in all antenna β-polypeptides of purple bacteria, were found: His-24 lies within the N-terminal hydrophilic domain and His-42 within the central hydrophobic domain. This polypeptide together with the previously described α-polypeptide form the basic structural unit of the B806–866 antenna complex from C. aurantiacus.
