Proton-coupled amino-acid transporter that mediates the transmembrane transport of L-histidine and some di- and tripeptides from inside the lysosome to the cytosol, and plays a key role in innate immune response ( ). Able to transport a variety of di- and tripeptides, including carnosine and some peptidoglycans (, ). Transporter activity is pH-dependent and maximized in the acidic lysosomal environment (By similarity). Involved in the detection of microbial pathogens by toll-like receptors (TLRs) and NOD-like receptors (NLRs), probably by mediating transport of bacterial peptidoglycans across the endolysosomal membrane: catalyzes the transport of certain bacterial peptidoglycans, such as muramyl dipeptide (MDP), the NOD2 ligand, and L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptanedioate (tri-DAP), the NOD1 ligand (, ). Required for TLR7, TLR8 and TLR9-mediated type I interferon (IFN-I) productions in plasmacytoid dendritic cells (pDCs) . Independently of its transporter activity, also promotes the recruitment of innate immune adapter TASL to endolysosome downstream of TLR7, TLR8 and TLR9: TASL recruitment leads to the specific recruitment and activation of IRF5 . Required for isotype class switch recombination to IgG2c isotype in response to TLR9 stimulation (By similarity). Required for mast cell secretory-granule homeostasis by limiting mast cell functions and inflammatory responses (By similarity).
Subcellular locations: Lysosome membrane, Endosome membrane, Early endosome membrane
Highly expressed in skeletal muscle. Moderately expressed in kidney, liver, and heart. Weakly expressed in colon and brain. Expressed in low levels throughout the gastrointestinal tract and in Caco-2 cells. Expressed in retinal fragment epithelium (RPE) and neural retina. Expressed in small intestine, stomach, duodenum, jejunum, ileum and colon.