title: Role of the core region of the PufX protein in inhibition of reconstitution of the core light-harvesting complexes of Rhodobacter sphaeroides and Rhodobacter capsulatus.
abstract: PufX, the protein encoded by the pufX gene of Rhodobacter capsulatus and Rhodobacter sphaeroides, has been further characterized. The mature forms of these proteins contain 9 and 12 fewer amino acids, respectively, at the C-terminal end of the protein than are encoded by their pufX genes. To identify the portion of PufX responsible for inhibition of LH1 formation in reconstitution experiments, different regions (N-terminus and several core regions containing different lengths of the C-terminus) of Rb. sphaeroides and Rb. capsulatus PufX were chemically synthesized. Neither the N- nor C-terminal polypeptides of Rb. sphaeroides were inhibitory to LH1 reconstitution. However, all core segments were active, causing 50% inhibition at a concentration ratio of between 3:1 and 6:1 relative to the LH1 alpha-polypeptides whose concentrations were 3-4 microM. CD measurements indicated that the core segment containing 39 amino acids of Rb. sphaeroides PufX exhibited 47% alpha-helix in trifluoroethanol while the core segment containing 43 amino acids of Rb. capsulatus PufX exhibited 59 and 55% alpha-helix in trifluoroethanol and in 0.80% octylglucoside in water, respectively. Approximately 50% alpha-helix was also indicated by a PHD (Burkhard-Rost) structure prediction. Binding of bacteriochlorophyll to these PufX core segments is implicated.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Cell Biology, Hogan Hall, Room 2-100, Northwestern University, Evanston, Illinois 60208-3500, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Parkes-Loach
authors.forename: C J
authors.initials: CJ
authors.lastname: Law
authors.forename: P A
authors.initials: PA
authors.lastname: Recchia
authors.forename: J
authors.initials: J
authors.lastname: Kehoe
authors.forename: S
authors.initials: S
authors.lastname: Nehrlich
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.forename: P A
authors.initials: PA
authors.lastname: Loach
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D001429:Bacteriochlorophylls / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D045342:Light-Harvesting Protein Complexes; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000302:isolation & purification / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016354:Rhodobacter capsulatus / Q000737:chemistry / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D010446:Peptide Fragments; D045322:Photosynthetic Reaction Center Complex Proteins; C088749:PufX protein, Rhodobacter; C094744:light-harvesting complex 1, Rhodospirillum