Dimeric chlorite dismutase from the nitrogen-fixing cyanobacterium Cyanothece sp. PCC7425.
It is demonstrated that cyanobacteria (both azotrophic and non-azotrophic) contain heme b oxidoreductases that can convert chlorite to chloride and molecular oxygen (incorrectly denominated chlorite 'dismutase', Cld). Beside the water-splitting manganese complex of photosystem II, this metalloenzyme is the second known enzyme that catalyses the formation of a covalent oxygen-oxygen bond. All cyanobacterial Clds have a truncated N-terminus and are dimeric (i.e. clade 2) proteins. As model protein, Cld from Cyanothece sp. PCC7425 (CCld) was recombinantly produced in Escherichia coli and shown to efficiently degrade chlorite with an activity optimum at pH 5.0 [kcat 1144 ± 23.8 s(-1), KM 162 ± 10.0 μM, catalytic efficiency (7.1 ± 0.6) × 10(6) M(-1) s(-1)]. The resting ferric high-spin axially symmetric heme enzyme has a standard reduction potential of the Fe(III)/Fe(II) couple of -126 ± 1.9 mV at pH 7.0. Cyanide mediates the formation of a low-spin complex with k(on)  = (1.6 ± 0.1) × 10(5) M(-1) s(-1) and k(off) = 1.4 ± 2.9 s(-1) (KD ∼ 8.6 μM). Both, thermal and chemical unfolding follows a non-two-state unfolding pathway with the first transition being related to the release of the prosthetic group. The obtained data are discussed with respect to known structure-function relationships of Clds. We ask for the physiological substrate and putative function of these O2 -producing proteins in (nitrogen-fixing) cyanobacteria.
Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, A-1190, Vienna, Austria.
Irene
I
Schaffner
Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, A-1190, Vienna, Austria.|Department for Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, Vienna, Austria.
Stefan
S
Hofbauer
Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, A-1190, Vienna, Austria.
Michael
M
Krutzler
Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, A-1190, Vienna, Austria.
Katharina F
KF
Pirker
Department of Life Sciences, University of Modena and Reggio Emilia, 41125, Modena, Italy.
Marzia
M
Bellei
Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, A-1190, Vienna, Austria.
Gerhard
G
Stadlmayr
Department for Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, Vienna, Austria.
Georg
G
Mlynek
Department for Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, Vienna, Austria.|Department of Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, 1000, Ljubljana, Slovenia.
Kristina
K
Djinovic-Carugo
Department of Chemistry and Geology, University of Modena and Reggio Emilia, 41125, Modena, Italy.
Gianantonio
G
Battistuzzi
Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, A-1190, Vienna, Austria.
Paul G
PG
Furtmüller
Department of Microbiology and Ecosystem Science, Division of Microbial Ecology, University of Vienna, Vienna, Austria.
Holger
H
Daims
Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, A-1190, Vienna, Austria.
Christian
C
Obinger
D055162:Biocatalysis; D002712:Chlorides / Q000378:metabolism*; D003486:Cyanides / Q000378:metabolism; D046889:Cyanothece / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D006418:Heme; D007700:Kinetics; D008958:Models, Molecular; D010088:Oxidoreductases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010802:Phylogeny; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D002712:Chlorides; D003486:Cyanides; D011994:Recombinant Proteins; D006418:Heme; D010088:Oxidoreductases; C402794:chlorite dismutase; D010100:Oxygen; C001599:chlorite