Proline transporter (PROT) belongs to a gene family of high affinity Na⁺- and Cl⁻-dependent plasma membrane transporters. PROT is a glycosylated protein encoded by the Slc6a7 gene. Its structure contains 12 putative transmembrane domains and is enriched in synaptosomal membrane fraction⁵.

PROT transporter is responsible for the active transporter of L-proline through the plasma membrane by using the transmembrane electrochemical ion gradients. Proline is co-transported with Na⁺ and Cl⁻ ions with a stoichiometry of 1:2:1^1-3_. 

Several studies have indicated that in the mammalian CNS, L-proline acts as a putative synaptic regulatory molecule. L-proline shows several properties that are common with characterized amino acid neurotransmitters⁴. Thus, PROT can be used as an important target for therapeutic and pathological alterations of synaptic function².

PROT transporter is expressed in subpopulations of putative glutamatergic pathways in the mammalian brain. Thus, PROT has a physiological role in excitatory neurotransmission.

Distribution of human PROT protein can be found in the corpus striatum suggesting that PROT is axonally transported from its site of biosynthesis to the nerve terminals in the striatum^4,5_.

Several recent studies have suggested that enkephalins competitively inhibit mammalian PROT through a direct interaction with the transporter protein at or near the substrate binding site¹.