Proton-coupled amino-acid transporter that transports oligopeptides of 2 to 4 amino acids with a preference for dipeptides (PubMed:8639691, PubMed:26320580). Transports the dipeptide-like aminopeptidase inhibitor bestatin (PubMed:8639691). Can also transport the aminocephalosporin antibiotic cefadroxil (By similarity). Also able to transport carnosine (By similarity). Involved in innate immunity by promoting the detection of microbial pathogens by NOD-like receptors (NLRs). Probably acts by mediating transport of bacterial peptidoglycans across the plasma membrane: catalyzes the transport of certain bacterial peptidoglycans, such as muramyl dipeptide (MDP), the NOD2 ligand (By similarity). a dipeptide(out) + H(+)(out) = a dipeptide(in) + H(+)(in) H(+)(out) + N-acetylmuramyl-L-alanyl-D-isoglutamine(out) = H(+)(in) + N-acetylmuramyl-L-alanyl-D-isoglutamine(in) carnosine(out) + H(+)(out) = carnosine(in) + H(+)(in) glycyl-sarcosine(out) + H(+)(out) = glycyl-sarcosine(in) + H(+)(in) Interacts (via extracellular domain region) with trypsin. Strongly expressed in kidney cortex and medulla. Also detected in brain, lung and spleen. The extracellular domain (ECD) region specifically binds trypsin. Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family.