Characterization of OpuA, a glycine-betaine uptake system of Lactococcus lactis.
A Lactococcus lactis glycine-betaine transport system was identified by functional complementation of an Escherichia coli proP proU mutant with a gene library from L. lactis sbsp. cremoris. The cloned locus forms an operon highly homologous to opuA, encoding a glycine-betaine uptake system of Bacillus subtilis. Disruption of opuA in L. lactis abolished protection by glycine-betaine against elevated osmolarity. OpuA belongs to the so-called "ABC transporters" family, which comprise an extracellularly localized substrate-binding protein. In B. subtilis OpuA system, this binding protein is a lipoprotein, attached to the external face of the cytoplasmic membrane by its lipidic moiety. In contrast, in the L. lactis opuA operon, and in other gram-positive homologues as well, a fusion between the gene encoding the integral membrane protein and the substrate-binding protein components gave rise to a hybrid protein presumably attaching the substrate-binding protein to the surface of the cell via its covalent link to the integral membrane component. Mapping of L. lactis opuA transcription start identified one mRNA, more abundant in cells grown at elevated osmolarity. Construction of an opuA-gusA fusion confirmed that opuA transcription is directed by a promoter osmotically inducible in L. lactis. When recombined upstream from a lac transcriptional fusion in the chromosome of E. coli, the opuA promoter appeared as very strong, and only poorly stimulated by elevated osmotic pressure, suggesting the existence of a specific machinery involved in the osmotic signal transduction in L. lactis.
Bouvier
J
J
Laboratoire de Microbiologie et Génétique Moléculaire, UPR 9007 du CNRS, Toulouse, France.
Bordes
P
P
Romeo
Y
Y
Fourçans
A
A
Bouvier
I
I
Gutierrez
C
C
D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism*; D000251:Adenosine Triphosphatases; D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D001622:Betaine / Q000378:metabolism*; D001693:Biological Transport, Active; D004269:DNA, Bacterial / Q000235:genetics; D013293:Enterococcus faecalis / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D016480:Helicobacter pylori / Q000235:genetics; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009995:Osmosis; D011401:Promoter Regions, Genetic; D017386:Sequence Homology, Amino Acid; D013297:Streptococcus pyogenes / Q000235:genetics
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D001622:Betaine; D000251:Adenosine Triphosphatases; C412743:OpuA protein, Lactococcus lactis