Substrate binding domain of putative molybdate-binding protein;the type 2 periplasmic binding protein fold.
This subfamily contains domains found in ModA proteins of putative ABC-type transporter. Molybdate transport system is comprised of a periplasmic binding protein, an integral membrane protein, and an energizer protein. These three proteins are coded by modA, modB, and modC genes, respectively. ModA proteins serve as initial receptors in the ABC transport of molybdate mostly in eubacteria and archaea. After binding molybdate with high affinity, they interact 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 ModA 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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