Polar amino acids-binding domain of ATP-binding cassette transporter-like systems that belong to the type 2 periplasmic binding fold protein superfamily.
This subfamily includes periplasmic binding domain of ATP-binding cassette transporter-like systems that serve as initial receptors in the ABC transport of amino acids and their derivatives in eubacteria. After binding their ligand 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 Abp proteins belong to the PBPI 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",