Substrate-binding protein OpuCC of ABC-type osmoregulatory transporter and related proteins; the type 2 periplasmic-binding protein fold
This subfamily includes the periplasmic substrate-binding protein OpuCC of the ABC transporter OpuC (where Opu is osmoprotectant uptake), which can recognize a broad spectrum of compatible solutes, and its paralog OpuBC that can solely bind choline. 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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