title: Subcellular localization of chlorosome proteins in Chlorobium tepidum and characterization of three new chlorosome proteins: CsmF, CsmH, and CsmX.
abstract: Chlorosomes are unique light-harvesting structures found in two families of photosynthetic bacteria. In this study, three chlorosome proteins (CsmF, CsmH, and CsmX) of the green sulfur bacterium Chlorobium tepidum were characterized by cloning and sequencing the genes which encode them, by overproducing the respective proteins in Escherichia coli, and by raising polyclonal antisera to the purified proteins. Three other proteins (AtpF, CT1970, and CT2144) which were identified in chlorosome fractions have similarly been characterized. The antisera were used to establish the distribution of each protein in various cellular fractions. Ten chlorosome proteins (CsmA, CsmB, CsmC, CsmD, CsmE, CsmF, CsmH, CsmI, CsmJ, and CsmX) copurified in a constant proportion together with bacteriochlorophyll c, and none of these 10 proteins was found in substantial amounts in other subcellular fractions. An antiserum to CsmH was highly effective in agglutinating chlorosomes, and antisera to CsmI, CsmJ, CsmX, and CsmA also immunoprecipitated chlorosomes to varying extents. However, an antiserum to CsmF did not agglutinate chlorosomes. The sequences of chlorosome proteins generally are not significantly similar to the sequences of other proteins in the databases. However, the N-terminal domains of three chlorosome proteins, CsmI, CsmJ, and CsmX, are related to adrenodoxin-type ferredoxins that ligate [2Fe-2S] clusters [Vassilieva, E. V., Antonkine, M. L., Zybailov, B. L., Yang, F., Jakobs, C. U., Golbeck, J. H., and Bryant, D. A. (2001) Biochemistry 40, 464-473]. The sequences of the C-terminal domains of these three proteins appear to be distantly related to CsmA and CsmE. The remaining chlorosome proteins can be divided into two additional structural families, CsmB/F and CsmC/D. CsmH is recovered in water-soluble form after overproduction in E. coli. Interestingly, this protein contains an N-terminal domain that is similar to CsmB/D, while its C-terminal domain is related to CsmC/D. The sequence relationships indicate that, although the protein composition of Chlorobium-type chlorosomes is superficially more complex than that of the chlorosomes of Chloroflexus aurantiacus, this heterogeneity is mostly produced by gene duplication and divergence among a small number of protein types.
authors.affiliation: Department of Biochemistry and Molecular Biology and Center for Biomolecular Structure and Function, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Elena V
authors.initials: EV
authors.lastname: Vassilieva
authors.forename: Veronica L
authors.initials: VL
authors.lastname: Stirewalt
authors.forename: Christiane U
authors.initials: CU
authors.lastname: Jakobs
authors.forename: Niels-Ulrik
authors.initials: NU
authors.lastname: Frigaard
authors.forename: Kaori
authors.initials: K
authors.lastname: Inoue-Sakamoto
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Baker
authors.forename: Anne
authors.initials: A
authors.lastname: Sotak
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry*; D019414:Chlorobi / Q000737:chemistry* / Q000378:metabolism; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D005260:Female; D015151:Immunoblotting; D007506:Iron-Sulfur Proteins; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008954:Models, Biological; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C419684:CsmX protein, Chlorobium tepidum; D007506:Iron-Sulfur Proteins; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D011994:Recombinant Proteins