1S3C: Arsenate Reductase C12s Mutant From E. Coli

Arsenic is a ubiquitous environmental toxic metal. Consequently, organisms detoxify arsenate by reduction to arsenite, which is then excreted or sequestered. The ArsC arsenate reductase from Escherichia coli plasmid R773, the best characterized arsenic-modifying enzyme, has a catalytic cysteine, Cys 12, in the active site, surrounded by an arginine triad composed of Arg 60, Arg 94, and Arg 107. During the reaction cycle, the native enzyme forms a unique monohydroxyl Cys 12-thiol-arsenite adduct that contains a positive charge on the arsenic. We hypothesized previously that this unstable intermediate allows for rapid dissociation of the product arsenite. In this study, the role of Arg 60 in product formation was evaluated by mutagenesis. A total of eight new structures of ArsC were determined at resolutions between 1.3 A and 1.8 A, with R(free) values between 0.18 and 0.25. The crystal structures of R60K and R60A ArsC equilibrated with the product arsenite revealed a covalently bound Cys 12-thiol-dihydroxyarsenite without a charge on the arsenic atom. We propose that this intermediate is more stable than the monohydroxyarsenite intermediate of the native enzyme, resulting in slow release of product and, consequently, loss of activity.
PDB ID: 1S3CDownload
MMDB ID: 31766
PDB Deposition Date: 2004/1/13
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 1.25  Å
Source Organism:
Similar Structures:
Biological Unit for 1S3C: monomeric; determined by author and by software (PQS)
Molecular Components in 1S3C
Label Count Molecule
Protein (1 molecule)
Arsenate Reductase
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

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