MPPA, A PERIPLASMIC BINDING-PROTEIN ESSENTIAL FOR IMPORT OF THE BACTERIAL-CELL WALL PEPTIDE L-ALANYL-GAMMA-D-GLUTAMYL-MESO-DIAMINOPIMELATE

Mutants of a diaminopimelic acid (Dap)-requiring strain of Escherichia coli were isolated which failed to grow on media in which Dap was rep laced by the cell wall murein tripeptide, L-alanyl-gamma-D-glutamyl-me so-diaminopimelate, In one such mutant, which is oligopeptide permease (Opp) positive, we have identified a new gene product, designated Mpp A (murein peptide permease A), that is about 46% identical to OppA, th e periplasmic binding protein for Opp, A plasmid carrying the wild-typ e mppA gene allows the mutant to grow on tripeptide, Two other mutants that failed to grow on tripeptide were resistant to triornithine toxi city, indicating a defect in the opp operon, An E. coli strain whose e ntire opp operon was deleted but which carried the mppA locus was unab le to grow on murein tripeptide unless it was provided with oppBCDF ge nes in trans, Our data suggest a model whereby the periplasmic MppA bi nds the murein tripeptide, which is then transported into the cytoplas m via membrane-bound and cytoplasmic OppBCDF, In assessing the affinit y of MppA for non-cell wall peptides, we have found that proline auxot rophy can be satisfied with the peptide Pro-Phe-Lys, which utilizes ei ther MppA or OppA in conjunction with OppBCDF for its uptake, Thus, Mp pA, OppA, and perhaps the third OppA paralog revealed by the E. coli g enome sequence may each bind a particular family of peptides but inter act with common membrane-associated components for transport of their bound ligands into the cell, As to the physiological function of MppA, the possibility that it may be involved in signal transduction pathwa y(s) is discussed.