ABSTRACT
Antenna polypeptides from two species of the family Ectothiorhodospiraceae have been investigated. By means of gel filtration and subsequent high-performance liquid chromatography, at least five polypeptides were isolated from each of Ectothiorhodospira halochloris and Ectothiorhodospira halophila. The majority of their primary structures was identified by Edman degradation. Comparison of these polypeptide sequences with the known primary structures of antenna polypeptides from various purple non-sulfur bacteria revealed interesting new aspects with regard to the structure of the core-peripheral antenna system. E. halochloris and E. halophila contain two pairs of alpha- and beta-polypeptides each with typical primary structure elements of core complexes, indicating a modified antenna complex organization.
Subject(s)
Bacteria/metabolism , Bacterial Proteins/genetics , Peptides/genetics , Alkylation , Amino Acid Sequence , Chromatography, Gel , Chromatography, High Pressure Liquid , Cyanogen Bromide , Light-Harvesting Protein Complexes , Molecular Sequence Data , Oxidation-Reduction , Peptides/metabolism , Photosynthetic Reaction Center Complex Proteins/metabolism , Sequence Homology, Nucleic Acid , Spectrum AnalysisABSTRACT
The antenna complex B880 of Rp. marina has been isolated by applying ion-exchange chromatography on Whatman DE-52 resin and sucrose density centrifugation of LDAO-solubilized photosynthetic membranes. The antenna polypeptides B880-alpha and B880-beta were prepared by organic solvent extraction of extensively dialyzed and freeze-dried B880 antenna complex material or photosynthetic membranes. Gel filtration on Sephadex LH-60 and ion-exchange chromatography on Whatman DE-32 resin in the presence of organic solvents and an additional step on a C-8 reversed phase column yielded pure alpha- and beta-apoproteins. Their complete primary structures have been elucidated using automated Edman degradation and carboxypeptidase digestion. According to quantitative Edman degradation the ratio of B880-alpha and B880-beta has been determined as 1:1 in the isolated antenna complex as well as in the photosynthetic membrane. B880-alpha of Rp. marina, presumably N-formylated, consists of 52 amino acid residues and is 75, 56, 52 and 44% homologous to the corresponding core antenna polypeptides of Rs. rubrum, Rp. viridis, Rb. capsulatus and Rb. sphaeroides. In contrast, B880-beta (56 amino acid residues) is less homologous to the corresponding core beta-antenna polypeptides of the same strains (57, 51, 41 and 42%). It shows an extended N-terminal domain as compared to the B880-alpha polypeptide. Apart from the typical structural features of bacterial membrane-bound antenna polypeptides (three domain structure. His-residue in the hydrophobic stretch) the antenna polypeptides of Rp. marina are structurally related to polypeptides of core antenna complexes with strong near infrared circular dichroism signals.
Subject(s)
Bacterial Proteins/isolation & purification , Rhodopseudomonas/metabolism , Amino Acid Sequence , Chromatography, Gel , Molecular Sequence Data , Peptide Fragments/analysis , Photosynthetic Reaction Center Complex Proteins , Species SpecificityABSTRACT
Spectrally pure B800-850 light harvesting complexes of Rhodopseudomonas acidophila 7750 were prepared by chromatography of LDAO-solubilised photosynthetic membranes on Whatmann DE-52 ion exchange resin. Two low molecular mass polypeptides (alpha, beta) have been isolated by organic solvent extraction of the lyophilised B800-850 light harvesting complexes. Their primary structures were determined by liquid phase sequencer runs, by the sequence analyses of C-terminal o-iodosobenzoic acid fragments, by hydrazinolysis and by carboxypeptidase degradation. B800-850 alpha consists of 53 amino acids and is 45.3% and 50.9% homologous to the B800-850-alpha antenna polypeptides of Rhodobacter sphaeroides and Rhodobacter capsulatus, respectively. The second very short polypeptide (B800-850-beta, 41 amino acids) is 61.0% and 56.1% homologous to the corresponding polypeptides of Rb. sphaeroides and Rb. capsulatus. The molar ratio of the two polypeptides is about 1:1. Both polypeptides show a hydrophilic N-terminal domain, a very hydrophobic central domain and a short C-terminal domain. In both polypeptides the typical His residues, identified in all antenna polypeptides of purple nonsulphur bacteria as possible bacteriochlorophyll binding sites, were found.
