Molecular cloning of PEPT 2, a new member of the H+/peptide cotransporter family, from human kidney

Biology of membrane transport proteins

Membrane transporter proteins are encoded by numerous genes that can be classified into several superfamilies, on the basis of sequence identity and biological function. Prominent examples include facilitative transporters, the secondary active symporters and antiporters driven by ion gradients, and active ABC (ATP binding cassette) transporters involved in multiple-drug resistance and targeting of antigenic peptides to MHC Class I molecules. Transported substrates range from nutrients and ions to a broad variety of drugs, peptides and proteins. Deleterious mutations of transporter genes may lead to genetic diseases or loss of cell viability. Transporter structure, function and regulation, genetic factors, and pharmaceutical implications are summarized in this review.

Proton/peptide cotransporter (PEPT 2) from human kidney: functional characterization and chromosomal localization

We report here on the functional characterization of the H+/peptide cotransporter PEPT 2 cloned from human kidney and on the chromosomal localization of the PEPT 2 gene. PEPT 2, when functionally expressed in HeLa cells, induces the transport of the neutral dipeptide glycylsarcosine. The induced transport activity is markedly influenced by extracellular pH. The optimum pH for the transport process is 6.0-7.0. Kinetic analysis has revealed that PEPT 2 is a high-affinity transporter, the Michaelis-Menten constant for glycylsarcosine being 74 +/- 14 microM. The human intestinal H+/peptide cotransporter PEPT 1 has 4-fold less affinity for the dipeptide under identical experimental conditions. Studies with other chemically diverse dipeptides have established that PEPT 2 possesses higher affinity than PEPT 1 not only for neutral peptides but also for peptides consisting of anionic and/or cationic amino acids. Somatic cell hybrid analysis and in situ hybridization have shown that the gene encoding PEPT 2 maps to human chromosome 3q13.3-q21.

Differential recognition of beta -lactam antibiotics by intestinal and renal peptide transporters, PEPT 1 and PEPT 2

This study was initiated to determine if there are differences in the recognition of beta -lactam antibiotics as substrates between intestinal and renal peptide transporters, PEPT 1 and PEPT 2. Reverse transcription-coupled polymerase chain reaction and/or Northern blot analysis have established that the human intestinal cell line Caco-2 expresses PEPT 1 but not PEPT 2, whereas the rat proximal tubule cell line SKPT expresses PEPT 2 but not PEPT 1. Detailed kinetic analysis has provided unequivocal evidence for participation of PEPT 2 in SKPT cells in the transport of the dipeptide glycylsarcosine and the aminocephalosporin cephalexin. The substrate recognition pattern of PEPT 1 and PEPT 2 was studied with cefadroxil (a cephalosporin) and cyclacillin (a penicillin) as model substrates for the peptide transporters constitutively expressed in Caco-2 cells (PEPT 1) and SKPT cells (PEPT 2). Cyclacillin was 9-fold more potent than cefadroxil in competing with glycylsacosine for uptake via PEPT 1. In contrast, cefadroxil was 13-fold more potent than cyclacillin in competing with the dipeptide for uptake via PEPT 2. The substrate recognition pattern of PEPT 1 and PEPT 2 was also investigated using cloned human peptide transporters functionally expressed in HeLa cells. Expression of PEPT 1 or PEPT 2 in HeLa cells was found to induce H(+)-coupled cephalexin uptake in these cells. As was the case with Caco-2 cells and SKPT cells, the uptake of glycylsarcosine induced in HeLa cells by PEPT 1 cDNA and PEPT 2 cDNA was inhibitable by cyclacillin and cefadroxil. Again, the PEPT 1 cDNA-induced dipeptide uptake was inhibited more potently by cyclacillin than by cefadroxil, and the PEPT 2 cDNA-induced dipeptide uptake was inhibited more potently by cefadroxil than by cyclacillin. It is concluded that there are marked differences between the intestinal and renal peptide transporters in the recognition of beta -lactam antibiotics as substrates.