Substrate-binding domain of quaternary amine ABC-type transporter; the type 2 periplasmic-binding protein fold
This group includes the periplasmic substrate-binding component of a putative quaternary amine ABC transport system that is predicted to be involved in uptake of osmoprotectants (also termed compatible solutes) such as betaine, choline, proline betaine, carnitine, and L-proline. The relative substrate preference of this group is not known. To counteract the efflux of water, many microorganisms accumulate the compatible solutes for a sustained adjustment to high osmolarity surroundings. This substrate-binding domain 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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