3SX6: Crystal Structure Of Sulfide:quinone Oxidoreductase Cys356ala Variant From Acidithiobacillus Ferrooxidans Complexed With Decylubiquinone

Sulfide:quinone oxidoreductase (SQR) is a peripheral membrane protein that catalyzes the oxidation of sulfide species to elemental sulfur. The enzymatic reaction proceeds in two steps. The electrons from sulfides are transferred first to the enzyme cofactor, FAD, which, in turn, passes them onto the quinone pool in the membrane. Several wild-type SQR structures have been reported recently. However, the enzymatic mechanism of SQR has not been fully delineated. In order to understand the role of the catalytically essential residues in the enzymatic mechanism of SQR we produced a number of variants of the conserved residues in the catalytic site including the cysteine triad of SQR from the acidophilic, chemolithotrophic bacterium Acidithiobacillus ferrooxidans. These were structurally characterized and their activities for each reaction step were determined. In addition, the crystal structures of the wild-type SQR with sodium selenide and gold(I) cyanide have been determined. Previously we proposed a mechanism for the reduction of sulfides to elemental sulfur involving nucleophilic attack of Cys356 on C(4A) atom of FAD. Here we also consider an alternative anionic radical mechanism by direct electron transfer from Cys356 to the isoalloxazine ring of FAD.
PDB ID: 3SX6Download
MMDB ID: 99640
PDB Deposition Date: 2011/7/14
Updated in MMDB: 2012/06
Experimental Method:
x-ray diffraction
Resolution: 1.8  Å
Source Organism:
Similar Structures:
Biological Unit for 3SX6: dimeric; determined by author and by software (PISA)
Molecular Components in 3SX6
Label Count Molecule
Proteins (2 molecules)
Sulfide-quinone Reductase, Putative
Molecule annotation
Chemicals (18 molecules)
* Click molecule labels to explore molecular sequence information.

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