ELECTROPHYSIOLOGICAL CHARACTERISTICS OF THE PROTON-COUPLED PEPTIDE TRANSPORTER PEPT2 CLONED FROM RAT-BRAIN

We have cloned a peptide transporter from rat brain and found it to be identical to rat kidney PEPT2. In the present study we characterize t he transport function of the rat brain PEPT2, with special emphasis on electrophysiological properties and interaction with N-acetyl-L-aspar tyl-L-glutamate (NAAG). When heterologously expressed in HeLa cells an d in SK-N-SH cells, PEPT2 transports several dipeptides but not free a mino acids in the presence of a proton gradient. NAAG competes with ot her peptides for the PEPT2-mediated transport process. When PEPT2 is e xpressed in Xenopus laevis oocytes, substrate-induced inward currents are detectable with dipeptides of differing charge in the presence of a proton gradient. Proton activation kinetics are similar for differen tly charged peptides. NAAG is a transportable substrate for PEPT2, as evidenced by NAAG-induced currents. The Hill coefficient for protons f or the activation of the transport of differently charged peptides, in cluding NAAG, is 1. Although the peptide-to-proton stoichiometry for n egatively charged peptides is 1, the transport nonetheless is associat ed with transfer of positive charge into the oocyte, as indicated by p eptide-induced inward currents.