SPECIFICITY OF PEPTIDE-TRANSPORT SYSTEMS IN LACTOCOCCUS-LACTIS - EVIDENCE FOR A 3RD SYSTEM WHICH TRANSPORTS HYDROPHOBIC DIPEPTIDES AND TRIPEPTIDES

A proton motive force-driven di-tripeptide carrier protein (DtpT) and an ATP-dependent oligopeptide transport system (Opp) have been describ ed for Lactococcus lactis MG1363. Using genetically well-defined mutan ts in which dtpT and/or opp were inactivated, we have now established the presence of a third peptide transport system (DtpP) in L. lactis. The specificity of DtpP partially overlaps that of DtpT, DtpP transpor ts preferentially di- and tripeptides that are composed of hydrophobic (branched-chain amino acid) residues, whereas DtpT has a higher speci ficity for more-hydrophilic and charged peptides. The toxic dipeptide L-phenylalanyl-beta-chloro-L-alanine has been used to select for a di- tripeptide transport-negative mutant with the Delta dtpT strain as a g enetic background, This mutant is unable to transport di- and tripepti des but still shows uptake of amino acids and oligopeptides, The DtpP system is induced in the presence of di- and tripeptides containing br anched-chain amino acids. The use of ionophores and metabolic inhibito rs suggests that, similar to Opp, DtpP-mediated peptide transport is d riven by ATP or a related energy-rich phosphorylated intermediate.