title: Structural basis for the oxidation of thiosulfate by a sulfur cycle enzyme.
abstract: Reduced inorganic sulfur compounds are utilized by many bacteria as electron donors to photosynthetic or respiratory electron transport chains. This metabolism is a key component of the biogeochemical sulfur cycle. The SoxAX protein is a heterodimeric c-type cytochrome involved in thiosulfate oxidation. The crystal structures of SoxAX from the photosynthetic bacterium Rhodovulum sulfidophilum have been solved at 1.75 A resolution in the oxidized state and at 1.5 A resolution in the dithionite-reduced state, providing the first structural insights into the enzymatic oxidation of thiosulfate. The SoxAX active site contains a haem with unprecedented cysteine persulfide (cysteine sulfane) coordination. This unusual post-translational modification is also seen in sulfurtransferases such as rhodanese. Intriguingly, this enzyme shares further active site characteristics with SoxAX such as an adjacent conserved arginine residue and a strongly positive electrostatic potential. These similarities have allowed us to suggest a catalytic mechanism for enzymatic thiosulfate oxidation. The atomic coordinates and experimental structure factors have been deposited in the PDB with the accession codes 1H31, 1H32 and 1H33.
authors.affiliation: Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences and School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: Vicki A
authors.initials: VA
authors.lastname: Bamford
authors.forename: Stefano
authors.initials: S
authors.lastname: Bruno
authors.forename: Tim
authors.initials: T
authors.lastname: Rasmussen
authors.forename: Corinne
authors.initials: C
authors.lastname: Appia-Ayme
authors.forename: Myles R
authors.initials: MR
authors.lastname: Cheesman
authors.forename: Ben C
authors.initials: BC
authors.lastname: Berks
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Hemmings
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D020560:Proteobacteria / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D013885:Thiosulfates / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D008024:Ligands; D013885:Thiosulfates; D006418:Heme; C017167:cytochrome C(551)