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Substrate binding domain of thiamin transporter, a member of the type 2 periplasmic binding fold superfamily. Thiamin-binding protein TbpA is the periplasmic component of ABC-type transporter in E. coli, while the transmembrane permease and ATPase are ThiP and ThiQ, respectively. Thiamin (vitamin B1) is an essential confactor in all living systems that most prokaryotes, plants, and fungi can synthesized thiamin. However, in vertebrates, thiamine cannot be synthesized and must therefore be obtained through dietary absorption. In addition to thiamin biosynthesis, most organisms can import thiamin using specific transporters. After binding thiamine with high affinity, TbpA interacts with a cognate membrane transport complex comprised of two integral membrane domains and two cytoplasmically located ATPase. This interaction triggers the ligand translocation across the cytoplasmic membrane energized by ATP hydrolysis. The thiamine-binding proteins belong to the PBP2 superfamily of periplasmic binding proteins that differ in size and ligand specificity, but have similar tertiary structures consisting of two globular subdomains connected by a flexible hinge. They have been shown to bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. |
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