ISSN:
1399-0047
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The arsenical resistance (ars) operon of the Escherichia coli plasmid R773 encodes a system for the active extrusion from cells of the toxic oxyanions arsenite (AsIIIO_{2}^{-}) and antimonite (SbIIIO_{2}^{-}) via an ATP-driven pump. The arsA and arsB genes of the operon encode the catalytic subunit (ATPase) and the membrane subunit of the pump, respectively. The arsC gene codes for a reductase that converts arsenate (AsVO_{4}^{3-}) to arsenite, thus extending bacterial resistance to the pentavalent state of arsenic. Crystals diffracting beyond 2.0 Å were obtained for the catalytic subunit of the pump (ArsA). These crystals belong to space group I222, with unit-cell parameters a ∼ 73, b ∼ 76, c ∼ 223 Å. A single molecule of ArsA, composed of two homologous halves, occupies the asymmetric unit of the I222 crystals with a predicted solvent content of 46%. Self-rotation function analysis suggests, however, that ArsA adopts a molecular packing corresponding to point group 422. One possible explanation of this result is that the two homologous halves of ArsA are related by a twofold axis of local symmetry and that the two halves of a `pseudo'-tetramer are related by a crystallographic twofold axis.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0907444999000256
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