Transporter that mediates the import of reduced folates and a subset of cyclic dinucleotides . Has high affinity for N5-methyltetrahydrofolate, the predominant circulating form of folate . Also able to mediate the import of antifolate drug methotrexate . Acts as an importer of immunoreactive cyclic dinucleotides, such as cyclic GMP-AMP (2'-3'-cGAMP), an immune messenger produced in response to DNA virus in the cytosol, and its linkage isomer 3'-3'-cGAMP . Mechanistically, acts as an antiporter, which export of intracellular organic anions to facilitate uptake of its substrates . 5-amino-4-imidazolecarboxamide riboside (AICAR), when phosphorylated to AICAR monophosphate, can serve as an organic anion for antiporter activity .
Cell membrane ; Multi-pass membrane protein . Apical cell membrane ; Multi-pass membrane protein . Basolateral cell membrane ; Multi-pass membrane protein .
Placenta, liver, and to a much smaller extent, in lung.
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