Substrate-binding domain of osmoregulatory ABC-type transporters; the type 2 periplasmic-binding protein fold
This family represents the periplasmic substrate-binding component of ABC transport systems that are involved in uptake of osmoprotectants (also termed compatible solutes) such as betaine, choline, proline betaine, carnitine, and L-proline. To counteract the efflux of water, bacteria and archaea 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",