Substrate-binding domain of cysteine- and aspartate/glutamate-binding proteins; the type 2 periplasmic-binding protein fold
This family comprises of the periplasmic-binding protein component of ABC transporters specific for cysteine and carboxylic amino acids, as well as their closely related proteins. The cysteine and aspartate-glutamate binding domains belong to the type 2 periplasmic binding protein fold superfamily (PBP2), whose many members are involved in chemotaxis and uptake of nutrients and other small molecules from the extracellular space as a primary receptor. The PBP2 proteins are typically comprised 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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