Substrate binding domain of Escherichia coli betaine transport system-like; the type 2 periplasmic binding protein fold
This group includes the periplasmic substrate-binding protein ProX. ProX from the Escherichia coli ATP-binding cassette transport system ProU binds the compatible solutes glycine betaine and proline betaine with high affinity and specificity. Many microorganisms accumulate these compatible solutes in response to high osmolarity to offset the loss of cell water. The ProX belongs to the type 2 periplasmic binding fold protein superfamily (PBP2). 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.
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