Specificity and selectivity determinants of peptide transport in Lactococcus lactis and other microorganisms.

Peptide transport in microorganisms is important for nutrition of the cell and various signalling processes including regulation of gene expression, sporulation, chemotaxis, competence and virulence development. Peptide transport is mediated via different combinations of ion-linked and ATP-binding cassette (ABC) transporters, the latter utilizing single or multiple peptide-binding proteins with overlapping specificities. The paradigm for research on peptide transport is Lactococcus lactis, in which the uptake of peptides containing essential amino acids is vital for growth on milk proteins. Differential expression and characteristics of peptide-binding proteins in several Lactococcus lactis strains resulted in apparent conflicts with older literature. Recent developments and new data now make the pieces of the puzzle fall back into place again and confirm the view that the oligopeptide-binding proteins determine the uptake selectivity of their cognate ABC transporters. Besides reviewing the current data on binding specificity and transport selectivity of peptide transporters in L. lactis, the possible implications for peptide utilization by other bacterial species are discussed.