Putative substrate binding domain of an ABC-type transporter similar to ThiY/THI5; the type 2 periplasmic binding protein fold.
This subfamily is phylogenetically similar to ThiY, which is the periplasmic N-formyl-4-amino-5-(aminomethyl)-2-methylpyrimidine (FAMP) binding component of the ABC transport system (ThiXYZ). FAMP is imported into cell by the transporter, where it is then incorporated into the thiamin biosynthetic pathway. The closest structural homologs of ThiY are THI5, which is responsible for the synthesis of 4-amino-5-(hydroxymethyl)-2-methylpyrimidine phosphate (HMP-P) in the thiamin biosynthetic pathway of eukaryotes, and periplasmic binding proteins involved in alkanesulfonate/nitrate and bicarbonate transport. After binding the ligand, they interact with a cognate membrane transport complex comprised of two integral membrane domains and two cytoplasmically located ATPase domains. This interaction triggers the ligand translocation across the cytoplasmic membrane energized by ATP hydrolysis. The ThiY/THI5 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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