Proton-coupled amino-acid transporter that transports oligopeptides of 2 to 4 amino acids with a preference for dipeptides (PubMed:11027540). Transports the dipeptide-like aminopeptidase inhibitor bestatin (By similarity). 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) (PubMed:29784761). 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 (PubMed:29784761). 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) Optimum pH is 6.0 or lower. Interacts (via extracellular domain region) with trypsin. Expressed in kidney brush border cells (at protein level) (PubMed:11027540). Highly expressed in macrophages (PubMed:29784761). The extracellular domain (ECD) region specifically binds trypsin. Decreased dipeptide uptake in bone marrow (PubMed:29784761). Decreased cytokine expression in response to LPS stimulation (PubMed:29784761). Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family.