The complete amino acid sequence of the bacteriochlorophyll c binding polypeptide from chlorosomes of the green photosynthetic bacterium Chloroflexus aurantiacus

Abstract

AbstractThe BChlc polypeptide was isolated from chlorosomes of the green bacterium Chloroflexus aurantiacus on Sephadex LH-60. The complete amino acid sequence of this 5.6 kDa polypeptide (51 amino acid residues) was determined. Most probably the 5.6 kDa polypeptide forms an α-helix between Trp 5 and Ile 42 with an asymmetrical (bipolar) distribution of polar amino acid residues along the helix axis: (i) At one side of the α-helix 5 Gln and 2 Asn residues are the possible binding sites for 7 BChlc molecules, (ii) On the other side Ser, Thr, His residues seem to be polypeptide-polypeptide interaction sites within the BChlc-protein complexes. It appears that the BChl-protein complex (chlorosome subunit, 5.2 × 6 nm) composed of 12 5.6 kDa polypeptides corresponds to the 'globular units' found by electron microscopy within the chlorosomes