Two oligopeptide transporters from Caenorhabditis elegans:molecular cloning and functional expression

Abstract

Two novel oligopeptide transporter cDNA clones, CPTA and CPTB, were identified by screening a Caenorhabditis elegans cDNA library using homology hybridization. The transporter proteins deduced from the cDNAs possess multiple transmembrane domains and reveal a moderate similarity to their mammalian counterparts in amino acid sequences. CPTA and CPTB, when expressed in Xenopus laevis oocytes and studied by both radiotracer flux and microelectrode voltage-clamp protocol, displayed a saturable electrogenic transport activity driven by a proton gradient with an overlapping broad spectrum of substrate specificity. Both transporters recognize di-, tri- and tetra-peptides including phenylalanylmethionylarginylphenylalaninamide (FMRFamide) and N-acetylaspartylglutamate, members of a large neuropeptide family commonly found throughout the animal kingdom. Kinetic analysis, however, revealed that CPTA and CPTB differed in their affinity for the peptide substrates, the former being a high-affinity type and the latter a low-affinity type. CPTA and CPTB are encoded by two distinct genes localized on separate chromosomes and are expressed during the whole life span of the organism.

A Novel H+-coupled Oligopeptide Transporter (OPT3) from Caenorhabditis elegans with a Predominant Function as a H+ Channel and an Exclusive Expression in Neurons

“…There is no identifiable transplicing leader sequence in the OPT3 cDNA. This indicates that the mRNA is directly transcribed from the opt3 gene, similar to the first two oligopeptide transporters (OPT1 and OPT2) previously reported (12).…”

“…The pellet was used for total RNA preparation. Total RNA was isolated from the C. elegans using TRIzol reagent from Life Technologies, Inc. Poly(A) ϩ mRNA was purified by a double affinity chromatography using oligo(dT)-cellulose (12).…”

“…Previously, two oligopeptide transporters (OPT) 1 from Caenorhabditis elegans, namely OPT1 and OPT2, homologous to the mammalian counterparts, PEPT1 and PEPT2, respectively, were identified, isolated, and characterized in our lab (12). Subsequently, a data base search revealed that there might be another OPT isoform encoded by the gene F56F4.5 on chromosome I in C. elegans.…”

Deletion of the Intestinal Peptide Transporter Affects Insulin and TOR Signaling in Caenorhabditis elegans

“…Although the deduced transporter proteins reveal only modest amino acid similarities with the mammalian proteins, the in vitro transport characteristics of the C. elegans and mammalian orthologues in Xenopus laevis oocytes are very similar (6). The C. elegans pep-2 gene encodes a protein with 36.9% amino acid sequence identity compared with the human PEPT1 and represents the low affinity/high capacity isoform of proton-coupled peptide transporters.…”

“…The Caenorhabditis elegans genome contains two homologues of the human pept1 and pept2 genes, designated pep-2 and pep-1 (aka opt-2 and opt-1, encoding CPTB and CPTA, respectively) (6). Although the deduced transporter proteins reveal only modest amino acid similarities with the mammalian proteins, the in vitro transport characteristics of the C. elegans and mammalian orthologues in Xenopus laevis oocytes are very similar (6).…”