Crystal structure of auracyanin, a "blue" copper protein from the green thermophilic photosynthetic bacterium Chloroflexus aurantiacus
Department of Chemistry and Biochemistry, Arizona State University, Phoenix, Arizona, United StatesJournal of Molecular Biology (Impact Factor: 4.33). 03/2001; 306(1):47-67. DOI: 10.1006/jmbi.2000.4201
Auracyanin B, one of two similar blue copper proteins produced by the thermophilic green non-sulfur photosynthetic bacterium Chloroflexus aurantiacus, crystallizes in space group P6(4)22 (a=b=115.7 A, c=54.6 A). The structure was solved using multiple wavelength anomalous dispersion data recorded about the CuK absorption edge, and was refined at 1.55 A resolution. The molecular model comprises 139 amino acid residues, one Cu, 247 H(2)O molecules, one Cl(-) and two SO(4)(2-). The final residual and estimated standard uncertainties are R=0.198, ESU=0.076 A for atomic coordinates and ESU=0.05 A for Cu---ligand bond lengths, respectively. The auracyanin B molecule has a standard cupredoxin fold. With the exception of an additional N-terminal strand, the molecule is very similar to that of the bacterial cupredoxin, azurin. As in other cupredoxins, one of the Cu ligands lies on strand 4 of the polypeptide, and the other three lie along a large loop between strands 7 and 8. The Cu site geometry is discussed with reference to the amino acid spacing between the latter three ligands. The crystallographically characterized Cu-binding domain of auracyanin B is probably tethered to the periplasmic side of the cytoplasmic membrane by an N-terminal tail that exhibits significant sequence identity with known tethers in several other membrane-associated electron-transfer proteins.
- "Moreover, different quinones (menaquinones or ubiquinones) are used to transport electrons to the cytochrome bc 1 complex in GSBs and purple bacteria (Fig. 2a). Like purple bacteria, FAPs also employ cyclic electron transport in the type II RC (P870), whereas an alternative complex III (ACIII), containing seven different protein subunits (Gao et al. 2010;Yanyushin et al. 2005), and auracyanin (a soluble blue-copper protein) (Bond et al. 2001;Lee et al. 2009) are utilized in place of the cytochrome bc 1 /b 6 f complex and cytochrome c 2 /plastocyanin, respectively, for photosynthetic electron transport (Fig. 2b). Finally, the electron transport pathway has not been completely established in the anaerobic anoxygenic heliobacteria that are obligatory photoheterotrophs and have the type I homodimeric RCs with a special pair of bacteriochlorophyll g absorbing at 798 nm (P798). "
Chapter: Photosynthetic Electron Transport
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- "The type I blue copper protein auracyanin, which has a single copper atom coordinated by two histidine, one cysteine and one methionine residues at the active site, is proposed to participate in the electron transfer from ACIII to the reaction center in Cfl. aurantiacus [35,47-49], and it has also been recently characterized in Roseiflexus castenholzii . Additionally, an auracyanin gene (trd_0373) has been identified in the genome of the non-photosynthetic bacterium Thermomicrobium roseum DSM 5159, which is evolutionally related to Cfl. aurantiacus . "
ABSTRACT: Chloroflexus aurantiacus is a thermophilic filamentous anoxygenic phototrophic (FAP) bacterium, and can grow phototrophically under anaerobic conditions or chemotrophically under aerobic and dark conditions. According to 16S rRNA analysis, Chloroflexi species are the earliest branching bacteria capable of photosynthesis, and Cfl. aurantiacus has been long regarded as a key organism to resolve the obscurity of the origin and early evolution of photosynthesis. Cfl. aurantiacus contains a chimeric photosystem that comprises some characters of green sulfur bacteria and purple photosynthetic bacteria, and also has some unique electron transport proteins compared to other photosynthetic bacteria. The complete genomic sequence of Cfl. aurantiacus has been determined, analyzed and compared to the genomes of other photosynthetic bacteria. Abundant genomic evidence suggests that there have been numerous gene adaptations/replacements in Cfl. aurantiacus to facilitate life under both anaerobic and aerobic conditions, including duplicate genes and gene clusters for the alternative complex III (ACIII), auracyanin and NADH:quinone oxidoreductase; and several aerobic/anaerobic enzyme pairs in central carbon metabolism and tetrapyrroles and nucleic acids biosynthesis. Overall, genomic information is consistent with a high tolerance for oxygen that has been reported in the growth of Cfl. aurantiacus. Genes for the chimeric photosystem, photosynthetic electron transport chain, the 3-hydroxypropionate autotrophic carbon fixation cycle, CO2-anaplerotic pathways, glyoxylate cycle, and sulfur reduction pathway are present. The central carbon metabolism and sulfur assimilation pathways in Cfl. aurantiacus are discussed. Some features of the Cfl. aurantiacus genome are compared with those of the Roseiflexus castenholzii genome. Roseiflexus castenholzii is a recently characterized FAP bacterium and phylogenetically closely related to Cfl. aurantiacus. According to previous reports and the genomic information, perspectives of Cfl. aurantiacus in the evolution of photosynthesis are also discussed. The genomic analyses presented in this report, along with previous physiological, ecological and biochemical studies, indicate that the anoxygenic phototroph Cfl. aurantiacus has many interesting and certain unique features in its metabolic pathways. The complete genome may also shed light on possible evolutionary connections of photosynthesis.
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ABSTRACT: This chapter introduces the blue copper-binding (BCB) domain-containing proteins based on the analysis of the genomic and expressed sequence tag (EST) sequence data, and presents the classification system. This classification is based on their ability to bind copper and the specific features of their domain organization. Members of the first three classes harbor single or multiple type 1, blue copper-binding sites, while members of the fourth class do not appear to bind copper. Some analysis of codon usage for conserved amino acids involved in copper binding will be used to trace the evolutionary history of the blue copper-binding (BCB) domains within a single genorne. The chapter also discusses the structural and physical characteristics of each kind of blue copper-binding (BCB) domain protein. The large number of blue copper-binding (BCB) domain proteins in plants may be explained by the phenomenon of genome duplication, believed to occur widely in the plant kingdom, as well as by different lateral gene transfers The blue copper-binding (BCB) domain-containing proteins evolved by gene duplication and fusion with other structural modules, resulting in diverse subcellular localization and the ability to carry out complex reactions that often differ from that of the ancestral protein. They are also modified by extensive amino acid substitutions and insertions.
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