Substrate-binding protein ProX of ABC-type osmoregulatory transporter from Archaeoglobus fulgidus and its related proteins; the type 2 periplasmic-binding protein fold
This subfamily includes the periplasmic substrate-binding protein ProX from the hyperthermophilic archaeon Archaeoglobus fulgidus and its related proteins. AfProX is involved in uptake of compatible solutes such as the trimethylammonium compound glycine betaine and the dimethylammonium compound proline betaine, but the relative substrate preference is not known. To counteract the efflux of water, many microorganisms accumulate the compatible solutes for a sustained adjustment to high osmolarity surroundings. AfProX 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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