Proton-coupled amino-acid transporter that transports oligopeptides of 2 to 4 amino acids with a preference for dipeptides (PubMed:7756356, PubMed:18367661). Transports the dipeptide-like aminopeptidase inhibitor bestatin (By similarity). Can also transport the aminocephalosporin antibiotic cefadroxil (By similarity). Also able to transport carnosine (PubMed:31073693). Involved in innate immunity by promoting the detection of microbial pathogens by NOD-like receptors (NLRs) (By similarity). 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. Expressed in kidney (PubMed:7756356). Not detected in intestine (PubMed:7756356). 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.