Important role in absorption of dietary peptides. High-affinity transporter of alanylalanine. Dipeptide transport activity is proton dependent. Optimum pH is 6. Expressed in thorax and abdomen of females: apical epithelial membranes of midgut, rectum, and reproductive tract. Also expressed in neuropil of the central nervous system, with elevated expression within the alpha- and beta-lobes of the mushroom bodies. Expressed both maternally and zygotically. Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family.