The type 2 periplasmic ligand-binding protein domain of the sensor-kinase BvgS and histidine kinase receptors, and related proteins
This family comprises the periplasmic sensor domain of the two-component sensor-kinase systems, such as the sensor protein BvgS of Bordetella pertussis and histidine kinase receptors (HisK), and uncharacterized related proteins. Typically, the two-component system consists of a membrane spanning sensor-kinase and a cytoplasmic response regulator. It serves as a stimulus-response coupling mechanism to enable microorganisms to sense and respond to changes in environmental conditions. The N-terminal sensing domain of the sensor kinase detects extracellular signals, such as small molecule ligands and ions, which then modulate the catalytic activity of the cytoplasmic kinase domain through a phosphorylation cascade. The periplasmic sensor domain belongs to the type 2 periplasmic-binding fold protein (PBP2) superfamily, whose members are involved in chemotaxis and uptake of nutrients and other small molecules from the extracellular space as a primary receptor. PBP2 typically comprises of two globular subdomains connected by a flexible hinge and bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. After binding their specific ligand with high affinity, they can interact with a cognate membrane transport complex comprised of two integral membrane domains and two receptor cytoplasmically-located ATPase domains. This interaction triggers the ligand translocation across the cytoplasmic membrane energized by ATP hydrolysis.
Jiyao W et al.(2023). "The conserved domain database in 2023.",