Substrate binding domain of iron and thiamine transporters-like, a member of the type 2 periplasmic binding fold superfamily.
The periplasmic iron binding protein plays an essential role in the iron uptake pathway of Gram-negative pathogenic bacteria from the Pasteurellaceae and Neisseriaceae families and is critical for survival of these pathogens within the host. On the other hand, thiamin is an essential cofactor in all living systems. Thiamin diphosphate (ThDP)-dependent enzymes play an important role in carbohydrate and branched-chain amino acid metabolism. Most prokaryotes, plants, and fungi can synthesize thiamin, but it is not synthesized in vertebrates. These periplasmic domains have high affinities for their respective substrates and serve as the primary receptor for transport. After binding iron and thiamine 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 iron- and thiamine-binding proteins belong to the PBPI2 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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