Characterization of the lactose-specific enzymes of the phosphotransferase system in Lactococcus lactis.
The plasmid-encoded lactose genes of the Lactococcus lactis phosphotransferase system encoding Enzyme IIIlac (lacF) and Enzyme IIlac (lacE) have been identified and cloned in Escherichia coli and L. lactis. Nucleotide sequence and transcription analysis showed that these genes are organized into a lactose-inducible operon with the gene order lacF-lacE-lacG-lacX, the latter two genes encoding phospho-beta-galactosidase and a 34-kDa protein with an unknown function, respectively. The lac-operon is immediately followed by an IS element that is homologous to ISS1. Enzyme IIIlac was purified from L. lactis and determination of its NH2-terminal sequence demonstrated that the lacF gene starts with a TTG codon and encodes a 105 amino acid protein (Mr = 11416). Cross-linking studies with the purified enzyme showed that Enzyme IIIlac is active as a trimer. A mutant lacF gene was identified in strain YP2-5 and appeared to encode Enzyme IIIlac containing the missense mutation G18E. The lacF gene could be expressed under control of vector-located promoter sequences resulting in overproduction of Enzyme IIIlac in E. coli and complementation of the L. lactis lacF mutant YP2-5. The deduced amino acid sequence of Enzyme IIlac consists of 586 amino acids (Mr = 61562) and shows the characteristics of a hydrophobic, integral membrane protein. The deduced primary structures of the L. lactis Enzyme IIIlac and Enzyme IIlac are homologous to those of Staphylococcus aureus (72 and 71% identity, respectively) and Lactobacillus casei (48 and 47% identity, respectively). In contrast, the organization of the lactose genes differs significantly between those Gram-positive bacteria. Heterogramic homology in specific domains was observed between the derived amino acid sequences of the lactose-specific enzymes and that of E. coli Enzyme IIIcel and Enzyme IIcel, which suggest a common function in the transport and phosphorylation of these structurally related beta-glucosides.
de Vos
W M
WM
Department of Biophysical Chemistry, Netherlands Institute for Dairy Research (NIZO), Ede.
Boerrigter
I
I
van Rooyen
R J
RJ
Reiche
B
B
Hengstenberg
W
W
D000595:Amino Acid Sequence; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D006026:Glycoside Hydrolases; D007780:Lacticaseibacillus casei / Q000235:genetics; D013294:Lactococcus lactis / Q000201:enzymology / Q000235:genetics*; D007785:Lactose / Q000378:metabolism*; D008969:Molecular Sequence Data; D009876:Operon; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics*; D010957:Plasmids; D011487:Protein Conformation; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D013211:Staphylococcus aureus / Q000235:genetics; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics*
D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C029022:phosphoenolpyruvate-lactose dependent phosphotransferase system; D006026:Glycoside Hydrolases; D001616:beta-Galactosidase; C022361:6-phospho-beta-galactosidase; D007785:Lactose