Crystal structure of chlorite dismutase, a detoxifying enzyme producing molecular oxygen.
Chlorite dismutase (Cld) is a key enzyme of perchlorate and chlorate respiration. This heme-based protein reduces the toxic compound chlorite into the innocuous chloride anion in a very efficient way while producing molecular oxygen. A sequence comparison between Cld homologues shows a highly conserved family. The crystal structure of Azospira oryzae strain GR-1 Cld is reported to 2.1 A resolution. The structure reveals a hexameric organization of the Cld, while each monomer exhibits a ferredoxin-like fold. The six subunits are organized in a ring structure with a maximal diameter of 9 nm and an inner diameter of 2 nm. The heme active-site pocket is solvent accessible both from the inside and the outside of the ring. Moreover, a second anion binding site that could accommodate the assumed reaction intermediate ClO(-) for further transformation has been identified near the active site. The environment of the heme cofactor was investigated with electron paramagnetic resonance spectroscopy. Apart from the high-spin ferric signal of the five-coordinate resting-state enzyme, two low-spin signals were found corresponding to six-coordinate species. The current crystal structure confirms and complements a recently proposed catalytic mechanism that proceeds via a ferryl species and a ClO(-) anion. Our structural data exclude cooperativity between the iron centers.
de Geus
Daniël C
DC
Department of Biophysical Structural Chemistry, Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands. d.de.geus@chem.leidenuniv.nl
Thomassen
Ellen A J
EA
Hagedoorn
Peter-Leon
PL
Pannu
Navraj S
NS
van Duijn
Esther
E
Abrahams
Jan Pieter
JP
D000595:Amino Acid Sequence; D055162:Biocatalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D011994:Recombinant Proteins; D010088:Oxidoreductases; C402794:chlorite dismutase; D010100:Oxygen