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CheC/CheX/FliY (CXY) family phosphatases The CXY family includes CheY-P-hydrolyzing proteins that function in bacterial chemotaxis, which involves cellular processes that control the movement of organisms toward favorable environments via rotating flagella, which in turn determines the sense of rotation by the intracellular response regulator CheY. When phosphorylated, CheY-P interacts directly with the flagellar motor, and this signal is terminated by the CXY family of phosphatases (Escherichia coli uses CheZ). CheC acts as a weak CheY-P phosphatase but increases activity in the presence of CheD. Bacillus subtilis has only CheC and FliY while many systems also have CheX. CheC and CheX appear to be primarily involved in restoring normal CheY-P levels, whereas FliY seems to act on CheY-P constitutively. Unlike CheC and CheX, FliY is localized in the flagellar switch complex, which also contains the stator-coupling protein FliG and the target of CheY-P, FliM. CheC, CheX, and FliY phosphatases share a consensus sequence ([DS]xxxExxNx(22)P) with four conserved residues thought to form the phosphatase active site. CheC class I and FliY each have two active sites, while CheC class II and III, and CheX have only one. This family also includes FliM, a component of the flagellar switch complex and a target of CheY, which lacks the phosphatase active site consensus sequence, and is not a CheY phosphatase. |
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