Putative sensor domain similar to BvgS; the type 2 periplasmic binding protein domain
BvgS is composed of two periplasmic domains homologous to bacterial periplasmic-binding proteins (PBPs), a transmembrane region followed successively by a cytoplasmic PAS (Per/ARNT/SIM), a Histidine-kinase (HK), a receiver and a Histidine phosphotransfer (Hpt) domains. The sensor protein BvgS can autophosphorylate and phosphorylate the response regulator BvgA. The BvgAS phosphorelay controls the expression of virulence factors in response to certain environmental stimuli in Bordetella pertussis. Its close homologs, Escherichia coli EvgS and Klebsiella pneumoniae KvgS, appear to be involved in the transcriptional regulation of drug efflux pumps and in countering free radical stresses and sensing iron limiting conditions, respectively. The periplasmic sensor domain of BvgS 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.
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