Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Cupins constitute a large and widespread superfamily ofb-barrel proteins in which a mononuclear metal site is both a conserved feature of the struc-ture and a source of functional diversity. Metal-binding residues are con-tributed from two core motifs that provide the signature for the superfamily. | ỊFEBS Journal Functional characterization of an orphan cupin protein from Burkholderia xenovorans reveals a mononuclear nonheme Fe2 -dependent oxygenase that cleaves b-diketones Stefan Leitgeb Grit D. Straganz and Bernd Nidetzky Institute of Biotechnology and BiochemicalEngineering Graz University of Technology Austria Keywords cupin nonheme iron oxygenase X-ray absorption spectroscopy b-diketone cleavage Correspondence Bernd Nidetzky Institute of Biotechnology and Biochemical Engineering Graz University of Technology Petersgasse 12 1 A-8010 Graz Austria Fax 43 316 873 8434 Tel 43 316 873 8400 E-mail bernd.nidetzky@tugraz.at Received 15 October 2008 revised 31 July 2009 accepted 17 August 2009 doi 10.1111 j.1742-4658.2009.07308.x Cupins constitute a large and widespread superfamily of b-barrel proteins in which a mononuclear metal site is both a conserved feature of the structure and a source of functional diversity. Metal-binding residues are contributed from two core motifs that provide the signature for the superfamily. On the basis of conservation of this two-motif structure we have identified an ORF in the genome of Burkholderia xenovorans that encodes a novel cupin protein Bxe_A2876 of unknown function. Recombinant Bxe_A2876 as isolated from Escherichia coli cell extract was a homotetramer in solution and showed mixed fractional occupancy of its 16.1 kDa subunit with metal ligands 0.06 copper 0.11 iron 0.17 zinc . Our quest for possible catalytic functions of Bxe_A2876 focused on Cu2 and Fe2 oxygenase activities known from related cupin enzymes. Fe2 elicited enzymatic catalysis of O2-dependent conversion of various b-dike-tone substrates via a nucleophilic mechanism of carbon-carbon bond cleavage. Data from X-ray absorption spectroscopy XAS support a five-coordinate or six-coordinate Fe2 center where the metal is bound by three imidazole nitrogen atoms at 1.98 A. Results of structure modeling studies suggest that His60 His62 and His102 are the coordinating .
