A PAS domain binds asparagine in the chemotaxis receptor McpB in Bacillus subtilis.

During chemotaxis toward asparagine by Bacillus subtilis, the ligand is thought to bind to the chemoreceptor McpB on the exterior of the cell and induce a conformational change. This change affects the degree of phosphorylation of the CheA kinase bound to the cytoplasmic region of the receptor. Until recently, the sensing domains of the B.

CheX in the three-phosphatase system of bacterial chemotaxis.

Bacterial chemotaxis involves the regulation of motility by a modified two-component signal transduction system. In Escherichia coli, CheZ is the phosphatase of the response regulator CheY but many other bacteria, including Bacillus subtilis, use members of the CheC-FliY-CheX family for this purpose. While Bacillus subtilis has only CheC and FliY, many systems also have CheX.