The Light-Harvesting Polypeptides ofRhodopseudomonas viridis.The Complete Amino-Acid Sequences of B1015-α, B1015-β and B1015-γ

Abstract

Three low molecular mass polypeptides have been isolated by using the technique of organic solvent extraction of thylakoid membranes or whole cells from Rhodopseudomonas viridis. Their primary structures were determined by long liquid phase sequencer runs, combined with the isolation and sequence analysis of the C-terminal o-iodosobenzoic acid fragment and carboxypeptidase degradation. The polypeptide which consists of 58 amino-acids and is 46% homologous to the antenna polypeptide B880-alpha from Rhodospirillum rubrum was designated as B1015-alpha (1 His residue). The sequence homology between the second polypeptide, named B1015-beta (55 amino acids, 2 His residues) and B880-beta from Rs. rubrum is 52%. For the third polypeptide consisting of 36 amino acids and exhibiting a high hydrophobicity, no equivalent polypeptide has so far been found in other purple bacteria. The molar ratio of these three organic solvent soluble polypeptides from Rp. viridis was estimated to be 1:1:1. Accordingly, the 36 amino-acid polypeptide is likely to be an additional constituent of the light-harvesting complex B1015, consequently termed as B1015-gamma. According to hydrophathy profiles, the transmembrane arrangement of B1015-alpha and B1015-beta within the thylakoid membrane is supposed to be similar. B1015-gamma, however, shows a somewhat different hydropathy profile. A particular feature of this polypeptide is its high amount of aromatic amino acids. It is postulated that B1015-gamma is involved in the formation of regular arrays of light-harvesting complexes.

Stoichiometric model of the photosynthetic unit of Ectothiorhodospira halochloris

“…The latter can be solubilized by extraction with methanol/chloroform, indicating a very hydrophobic character. Previously this small protein had been observed only in membranes of R. viridis; despite its different staining it is thought to occur in equimolar amounts with respect to the a and 8 polypeptides (17). The apparent molecular masses of the LH polypeptides are in good agreement with the sequence data of the corresponding proteins from R. viridis (4.00, 6.14, and 6.85 kDa) (17).…”

Localization of the exposed N-terminal region of the B800-850 alpha and beta light-harvesting polypeptides on the cytoplasmic surface of Rhodopseudomonas capsulata chromatophores

“…The amino acid sequence of the B800-850 a polypeptide of R. capsulata (6,22) is very homologous to those of the B800-850 a polypeptide of Rhodopseudomonas sphaeroides (24) and the B1015 a polypeptide of Rhodopseudomonas viridis (2). This is true not only for the hydrophobic membrane-spanning part but also for the N-terminal region exposed on the cytoplasmic surface.…”

“…This is true not only for the hydrophobic membrane-spanning part but also for the N-terminal region exposed on the cytoplasmic surface. The P chains of the light-harvesting complexes are also homologous to each other but not to the a chains (2,19,23,24). The histidine residues (His-31 in B800-850 a and His-38 in B800-850 a of R. capsulata) are localized in a central hydrophobic domain (Fig.…”

“…The histidine residues (His-31 in B800-850 a and His-38 in B800-850 a of R. capsulata) are localized in a central hydrophobic domain (Fig. 4) and are very much conserved in all of the a and a chains which have been analyzed (2,3,5,19,22,24).…”

A new possible binding site for bacteriochlorophyll b in a light‐harvesting polypeptide of the bacterium Ectothiorhodospira halochloris

“…A B800/1020 antenna complex has been isolated and characterized [5] as consisting of three polypeptides differing in size [4,5]. In the case of purple non-sulfur bacteria a great number of lightharvesting polypeptides from various species have been isolated and their primary structures have been determined [13][14][15][16][17][18][19][20]. These antenna polypeptides exhibit a histidine residue in the central hydrophobic domain, assigned as the fifth ligand to the Mg atom of bacteriochlorophyll.…”