PMID:22176720

Citation	Liu, G, Liu, M, Kim, EH, Maaty, WS, Bothner, B, Lei, B, Rensing, C, Wang, G and McDermott, TR (2012) A periplasmic arsenite-binding protein involved in regulating arsenite oxidation. Environ. Microbiol. 14:1624-34
Abstract	Arsenic (As) is the most common toxic element in the environment, ranking first on the Superfund List of Hazardous Substances. Microbial redox transformations are the principal drivers of As chemical speciation, which in turn dictates As mobility and toxicity. Consequently, in order to manage or remediate environmental As, land managers need to understand how and why microorganisms react to As. Studies have demonstrated a two-component signal transduction system comprised of AioS (sensor kinase) and AioR (response regulator) is involved in regulating microbial AsIII oxidation, with the AsIII oxidase structural genes aioB and aioA being upregulated by AsIII. However, it is not known whether AsIII is first detected directly by AioS or by an intermediate. Herein we demonstrate the essential role of a periplasmic AsIII-binding protein encoded by aioX, which is upregulated by AsIII. An ΔaioX mutant is defective for upregulation of the aioBA genes and consequently AsIII oxidation. Purified AioX expressed without its TAT-type signal peptide behaves as a monomer (MW 32 kDa), and Western blots show AioX to be exclusively associated with the cytoplasmic membrane. AioX binds AsIII with a K(D) of 2.4 µM AsIII; however, mutating a conserved Cys108 to either alanine or serine resulted in lack of AsIII binding, lack of aioBA induction, and correlated with a negative AsIII oxidation phenotype. The discovery and characterization of AioX illustrates a novel AsIII sensing mechanism that appears to be used in a range of bacteria and also provides one of the first examples of a bacterial signal anchor protein.
Links	PubMed Online version:10.1111/j.1462-2920.2011.02672.x
Keywords	Agrobacterium tumefaciens/genetics; Agrobacterium tumefaciens/metabolism; Arsenites/metabolism; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Escherichia coli/genetics; Escherichia coli/metabolism; Gene Expression Regulation, Bacterial; Oxidation-Reduction; Oxidoreductases/genetics; Oxidoreductases/metabolism; Periplasmic Binding Proteins/metabolism; Sequence Deletion; Signal Transduction
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
RHIRD:G8XNW6		GO:0098562: cytoplasmic side of membrane	ECO:0000314:		C		In Figure 2 a western blot analysis shows that AioX is associated with the cytoplasmic membrane.	complete CACAO 10793
RHIRD:G8XNW6	Contributes to	GO:0046872: metal ion binding	ECO:0000314:		F		Gel filtration chromatography data suggests that AioX interacts with AsIII (figure 4). In figure 5A ICP-MS analysis directly demonstrates AsIII binding to AioX. Figure 5B fluorescence quenching data suggests the formation of an AioX–AsIII complex.	complete CACAO 10794
RHIRD:G8XNW6	Contributes to	GO:0030613: oxidoreductase activity, acting on phosphorus or arsenic in donors	ECO:0000315:		F		In figure 1 the AsIII oxidation profiles of wild type and mutant delta aioX and M53 mutants suggest that AioX participates to AsIII oxidation in Agrobacterium tumefaciens.	complete CACAO 10795

References

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