An Arabidopsis Peptide Transporter Is a Member of a New Class of Membrane Transport Proteins

Abstract

An Arabidopsis peptide transport gene was cloned from an Arabidopsis cDNA library by functionally complementing a yeast peptide transport mutant. The Arabidopsis plant peptide transporter (AtPTR2) allowed growth of yeast cells on dipeptides and tripeptides but not peptides four residues and higher. The plant peptide transporter also conferred sensitivity to a number of ethionine-containing, toxic peptides of chain length three or less and restored the ability to take up radiolabeled dileucine at levels similar to that of the wild type. Dileucine uptake was reduced by the addition of a variety of growth-promoting peptides. The sequence of a cDNA insert of 2.8 kb indicated an open reading frame encoding a 610-amino acid polypeptide (67.5 kD). Hydropathy analysis predicted a highly hydrophobic protein with a number of potential transmembrane segments. At the amino acid level, the Arabidopsis plant peptide transporter shows 24.6, 28.5, and 45.2% identity to the Arabidopsis nitrate-inducible nitrate transporter (CHL1), the rabbit small intestine oligopeptide transporter (PepT1), and the yeast peptide transporter (Ptr2p), respectively, but little identity to other proteins known to be involved in peptide transport. Root growth of Arabidopsis seedlings exposed to ethionine-containing toxic peptides was inhibited, and growth was restored by the addition of certain peptides shown to compete with dileucine uptake in yeast expressing the Arabidopsis transport gene. Consistent with the observed inhibition of root growth by toxic peptides, the peptide transporter is expressed in the roots of Arabidopsis seedlings. This study represents the characterization of a plant peptide transporter that is a member of a new class of related membrane transport proteins.

Expression cloning and functional characterization of the kidney cortex high-affinity proton-coupled peptide transporter.

“…However, the significant identity is predominantly found in the membrane-spanning domains, whereas the large extracellular loop, which contains 210 amino acid residues, shows only a 21% sequence match. Comparisons with nonmammalian POT family members like the nitrate transporter CHL1 from Arabidopsis thaliana (21) and the peptide permease PTR2 from Saccharomyces cerevisiae (22) reveal much lower sequence similarities.…”

Mechanisms and Functional Properties of Two Peptide Transporters, AtPTR2 and fPTR2

“…The ϳ2.0-kb NotI cDNA fragment of AtPTR2 or fPTR2 was excised from plasmids pDTF1 (6) or pDTF4 (13), respectively, and cloned into pBluescript SKϩ (Stratagene, La Jolla, CA) to produce the restriction sites for the subsequent construction. For AtPTR2, the cDNA fragment containing 25 bp of the 5Ј untranslated region, 1758 bp of the coding region, and 141 bp of the 3Ј untranslated region were generated by digestion with EcoRI and XhaI (both in the multiple cloning site) and cloned into the EcoRI and XhaI sites of pGEMHE to give plasmid pGEMHE-AtPTR2.…”

“…In situ hybridization analysis showed that AtPTR2 is expressed in the embryo (12). The peptide transporter gene fPTR2 (originally named AtPTR2A) was also isolated by functional complementation of a yeast peptide transport mutant using an Arabidopsis cDNA library (13), but was later found not to be an Arabidopsis gene, but probably derived from a fungal contaminant (14).…”

Nitrate transporters and peptide transporters

“…In 1994, five di/tripeptide transporter genes were identified independently in the rabbit (PepT1) [4], a fungus (fPTR2) [5,6], Arabidopsis (AtNTR1, renamed as AtPTR2) [7,8], yeast (PTR2) [9] and a bacterium (DtpT) [10] by functional cloning based on peptide transport activity when expressed in Xenopus oocytes (PepT1), complementation of a yeast mutant (fPTR2, AtPTR2 and yeast PTR2), or complementation of an Escherichia coli mutant (DtpT). These peptide transporters were found to share sequence similarity with the nitrate transporter CHL1, and, together, they form a new transporter family, called NRT1 (PTR).…”

“…Functional analysis of AtPTR2 and fungus fPTR2 (formerly AtPTR2-A, isolated by complementing a yeast mutant with an Arabidopsis cDNA library, but later found to be a gene from a fungal contaminant [5,6]) in Xenopus oocytes under voltage clamp conditions revealed that both transport a broad spectrum of dipeptides, with K m s ranging from 30 lM to 3 mM [14]. Similar to rabbit PepT1, AtPTR2 and fPTR2 prefer dipeptides; the tripeptide and amino acid transport activities being $60% and 10%, respectively, of the dipeptide activity [14].…”