title: Characterization of the FMO protein from the aerobic chlorophototroph, Candidatus Chloracidobacterium thermophilum.
abstract: Candidatus Chloracidobacterium (Cab.) thermophilum is a recently discovered aerobic chlorophototroph belonging to the phylum Acidobacteria. From analyses of genomic sequence data, this organism was inferred to have type-1 homodimeric reaction centers, chlorosomes, and the bacteriochlorophyll (BChl) a-binding Fenna-Matthews-Olson protein (FMO). Here, we report the purification and characterization of Cab. thermophilum FMO. Absorption, fluorescence emission, and CD spectra of the FMO protein were measured at room temperature and at 77 K. The spectroscopic features of this FMO protein were different from those of the FMO protein of green sulfur bacteria (GSB) and suggested that exciton coupling of the BChls in the FMO protein is weaker than in FMO of GSB especially at room temperature. HPLC analysis of the pigments extracted from the FMO protein only revealed the presence of BChl a esterified with phytol. Despite the distinctive spectroscopic properties, the residues known to bind BChl a molecules in the FMO of GSB are well conserved in the primary structure of the Cab. thermophilum FMO protein. This suggests that the FMO of Cab. thermophilum probably also binds seven or possibly eight BChl a(P) molecules. The results imply that, without changing pigment composition or structure dramatically, the FMO protein has acquired properties that allow it to perform light harvesting efficiently under aerobic conditions.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tsukatani
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Wen
authors.forename: Robert E
authors.initials: RE
authors.lastname: Blankenship
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
mesh_terms: D000332:Aerobiosis; D000595:Amino Acid Sequence; D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D008024:Ligands; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010860:Pigments, Biological / Q000378:metabolism; D016415:Sequence Alignment; D013050:Spectrometry, Fluorescence
chemical_list: D001426:Bacterial Proteins; C086320:FMO bacteriochlorophyll protein, Bacteria; D008024:Ligands; D045342:Light-Harvesting Protein Complexes; D010860:Pigments, Biological