Cloning and functional expression in Escherichia coli of the gene encoding the di- and tripeptide transport protein of Lactobacillus helveticus.

The gene encoding the di- and tripeptide transport protein (DtpT) of Lactobacillus helveticus (DtpTLH) was cloned with the aid of the inverse PCR technique and used to complement the dipeptide transport-deficient and proline-auxotrophic Escherichia coli E1772. Functional expression of the peptide transporter was shown by the uptake of prolyl-[14C] alanine in whole cells and membrane vesicles. Peptide transport via DtpT in membrane vesicles is driven by the proton motive force. The system has specificity for di- and tripeptides but not for amino acids or tetrapeptides. The dtpTLH gene consists of 1,491 bp, which translates into a 497-amino-acid polypeptide. DtpTLH shows 34% identity to the di- and tripeptide transport protein of Lactococcus lactis and is also homologous to various peptide transporters of eukaryotic origin, but the similarity between these proteins is confined mainly to the N-terminal halves.