Peptide-binding protein and related homologs; type 2 periplasmic binding protein fold
This domain is found in solute binding proteins that serve as initial receptors in the ABC transport, signal transduction and channel gating. The PBP2 proteins share the same architecture as periplasmic binding proteins type 1, but have a different topology. They are typically comprised of two globular subdomains connected by a flexible hinge and bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. The majority of PBP2 proteins function in the uptake of small soluble substrates in eubacteria and archaea. After binding their specific ligand with high affinity, they can 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. Besides transport proteins, the family includes ionotropic glutamate receptors and unorthodox sensor proteins involved in signal transduction.
Jiyao W et al.(2023). "The conserved domain database in 2023.",