title: Biochemical characterization of the dissociated forms from the core antenna proteins from purple bacteria.
abstract: The core light-harvesting protein from Rhodospirillum rubrum is of particular interest for studying membrane polypeptide association, as it can be reversibly dissociated in the presence of n-octyl-beta-D-glucopyranoside (betaOG) into smaller subunit forms, which exhibit dramatically blue-shifted absorption properties (Miller et al. (1987) Biochemistry 26, 5055-5062). During this dissociation/reassociation process, two main spectroscopic forms are observed, absorbing at 820 (B820) and 777 (B777) nm, respectively. By using polyacrylamide gel electrophoresis in the presence of betaOG, these forms were characterized from a biochemical point of view. B777 consist of a mixture of alpha or beta polypeptide chains, retaining their bound bacteriochlorophyll (BChl) molecules. The absorption properties of the BChl molecules bound to the monomeric polypeptides do not depend on the chemical nature of the polypeptides they are bound to. B820 is more complex and consist of equilibrium between alphabeta-containing oligomers and beta only containing dimers, all exhibiting very similar electronic absorption properties. Resonance Raman spectroscopy indicates that the binding site provided by the beta-only B820 to the BChl molecules is very similar to that provided by the alphabeta B820. This, together with the observation that the alpha polypeptide alone is unable to form B820, suggests that the local organization of the BChl molecules tightly depends on BChl-protein interactions. On the other hand, our results suggest that the affinity of the beta-BChl complexes for itself and for the alpha-BChl ones are of the same order of magnitude, the formation of heterodimeric complexes being mainly driven by the inability of alpha-BChl complexes to self-associate.
authors.affiliation: Section de Biophysique des Fonctions Membranaires, DBJC/CEA and URA CNRS 2096, C.E. Saclay, 91191 Gif sur Yvette Cedex, France. Veronique.Arluison@ibpc.fr
authors.forename: Véronique
authors.initials: V
authors.lastname: Arluison
authors.forename: Jérôme
authors.initials: J
authors.lastname: Seguin
authors.forename: Bruno
authors.initials: B
authors.lastname: Robert
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D002021:Buffers; D004591:Electrophoresis, Polyacrylamide Gel; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D021122:Protein Subunits; D012247:Rhodospirillum rubrum / Q000737:chemistry* / Q000378:metabolism*; D012996:Solutions; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013059:Spectrum Analysis, Raman; D014325:Tromethamine / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D002021:Buffers; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D021122:Protein Subunits; D012996:Solutions; C094744:light-harvesting complex 1, Rhodospirillum; D014325:Tromethamine; D005998:Glycine; C100184:tricine