Structural Insight of Arsenate Reductase in Chrysiogenes arsenatis, ArrX
1Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne 3086, Australia.
2Division of Biosciences, University College London, London WC1E 6BT, United Kingdom.
Arsenic is a naturally occurring toxic metalloid that is found in earth’s crust, soil, rocks, surface waters and oceans. Ingestion of arsenic through drinking water and food and through the inhalation of dust particles is the most common method of exposure to arsenic. Microorganisms play an important role in transforming arsenic in the environment (Gadd, 2000), with the potential for bacterial respiration to contribute to environmental decontamination.
Arsenic can exist in both organic and inorganic forms with four oxidation states: arsines and methyl arsines (As-3), elemental arsenic (As0), arsenite (AsO33-) and arsenate (AsO43-) (Polizzotto, Harvey, Sutton, & Fendorf, 2005). The bacterium Chrysiogenes arsenatis is able to respire with arsenate (V). Its reduction to arsenite (III) being catalysed by the Arr system. ArrX, is a periplasmic binding protein that binds arsenate and triggers the expression of the arsenate reductase proteins ArrA and ArrB. ArrX binds arsenate specifically, which with a sensory histidine kinase activates the signalling transduction for the expression of arrAB operon (Krafft & Macy, 1998). This presentation will describe the crystal structure of the ArrX protein to determine the structural basis of its substrate specificity in order to understand the mechanism of this signalling system.
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