Proton-coupled amino-acid transporter that transports oligopeptides of 2 to 4 amino acids with a preference for dipeptides (PubMed:7896779, PubMed:18367661, PubMed:19685173). Primarily responsible for the absorption of dietary di- and tripeptides from the small intestinal lumen (By similarity). a dipeptide(out) + H(+)(out) = a dipeptide(in) + H(+)(in) an L-amino acid tripeptide(out) + H(+)(out) = an L-amino acid tripeptide(in) + H(+)(in) glycyl-sarcosine(out) + H(+)(out) = glycyl-sarcosine(in) + H(+)(in) H(+)(out) + L-alanyl-L-proline(out) = H(+)(in) + L-alanyl-L-proline(in) H(+)(out) + L-leucyl-L-proline(out) = H(+)(in) + L-leucyl-L-proline(in) glycyl-L-proline(out) + H(+)(out) = glycyl-L-proline(in) + H(+)(in) H(+)(out) + L-alanyl-L-prolylglycine(out) = H(+)(in) + L-alanyl-L-prolylglycine(in) glycylglycyl-L-isoleucine(out) + H(+)(out) = glycylglycyl-L-isoleucine(in) + H(+)(in) glycylglycyl-L-proline(out) + H(+)(out) = glycylglycyl-L-proline(in) + H(+)(in) Interacts (via extracellular domain region) with trypsin. 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.