Proton-coupled transporter that delivers pathogen-associated or danger-associated molecular patterns to cytosolic pattern recognition receptors as part of the innate immune response to microbes or tissue injury (PubMed:28539433, PubMed:34235268). Has selectivity toward muropeptides that contain the amino acid diaminopimelic acid (DAP-type peptidoglycan muropeptides) including Tri-DAP and tracheal toxin (TCT), common in Gram-negative bacteria and Gram-positive bacilli. In the context of immune recognition of skin microbiota, shuttles bacterial muropeptides across the endolysosomal membranes into the cytosol for recognition by NOD1, triggering MYD88-dependent secretion of IL1A and neutrophil recruitment in a pyroptosis-type inflammatory process (PubMed:28539433). To a lesser extent and redundantly, transports muramyl dipeptides derived from most bacterial proteoglycans, eliciting NOD2 receptor activation and downstream inflammatory responses (PubMed:28539433). Postulated to function as a dominant importer of cyclic GMP-AMP dinucleotides (cGAMPs) in monocyte and macrophage cell lineages. Selectively imports cGAMPs derived from pathogenic bacteria such as 3’3′-cGAMP thus providing for differential immune recognition of pathogenic versus commensal bacteria. During tumorigenesis may transport extracellular tumor-derived 2’3′-cGAMP across the plasma membrane of M1-polarized macrophages to activate the anti-tumoral stimulator of interferon genes (STING) pathway (PubMed:34235268). The transport mechanism, its electrogenicity and stoichiometry remain to be elucidated (Probable).
