The periplasmic substrate-binding component of an uncharacterized active transport system closely related to spermidine and putrescine transporters; contains the type 2 periplasmic binding fold.
This group represents the periplasmic binding domain that serves as a primary polyamine receptor of an uncharacterized ABC-type transport system from plants and plant-symbiotic cyanobacteria. Polyamine transport plays an essential role in the regulation of intracellular polyamine levels which are known to be elevated in rapidly proliferating cells and tumors. Natural polyamines are putrescine, spermindine, and spermine. They are polycations that play multiple roles in cell growth, survival and proliferation, as well as plant stress and disease resistance. They can interact with negatively charged molecules, such as nucleic acids, to modulate their functions. Members of this family belong to the type 2 periplasmic-binding fold superfamily. PBP2 is 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.
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