Dual role of alpha-acetolactate decarboxylase in Lactococcus lactis subsp. lactis.
The alpha-acetolactate decarboxylase gene aldB is clustered with the genes for the branched-chain amino acids (BCAA) in Lactococcus lactis subsp. lactis. It can be transcribed with BCAA genes under isoleucine regulation or independently of BCAA synthesis under the control of its own promoter. The product of aldB is responsible for leucine sensibility under valine starvation. In the presence of more than 10 microM leucine, the alpha-acetolactate produced by the biosynthetic acetohydroxy acid synthase IlvBN is transformed to acetoin by AldB and, consequently, is not available for valine synthesis. AldB is also involved in acetoin formation in the 2,3-butanediol pathway, initiated by the catabolic acetolactate synthase, AlsS. The differences in the genetic organization, the expression, and the kinetics parameters of these enzymes between L. lactis and Klebsiella terrigena, Bacillus subtilis, or Leuconostoc oenos suggest that this pathway plays a different role in the metabolism in these bacteria. Thus, the alpha-acetolactate decarboxylase from L. lactis plays a dual role in the cell: (i) as key regulator of valine and leucine biosynthesis, by controlling the acetolactate flux by a shift to catabolism; and (ii) as an enzyme catalyzing the second step of the 2,3-butanediol pathway.
Goupil-Feuillerat
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N
Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, Jouy en Josas, France.
Cocaign-Bousquet
M
M
Godon
J J
JJ
Ehrlich
S D
SD
Renault
P
P
D000093:Acetoin / Q000378:metabolism; D000095:Acetolactate Synthase / Q000378:metabolism; D000595:Amino Acid Sequence; D000597:Amino Acids, Branched-Chain / Q000096:biosynthesis*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002262:Carboxy-Lyases / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D007532:Isoleucine / Q000096:biosynthesis; D007773:Lactates / Q000378:metabolism; D013294:Lactococcus lactis / Q000201:enzymology* / Q000235:genetics; D007930:Leucine / Q000096:biosynthesis / Q000494:pharmacology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D019289:Pyruvic Acid / Q000378:metabolism; D014158:Transcription, Genetic; D014633:Valine / Q000096:biosynthesis
C108615:AldR protein, Lactococcus lactis; D000597:Amino Acids, Branched-Chain; D001426:Bacterial Proteins; D007773:Lactates; D007532:Isoleucine; C006359:alpha-acetolactate; D019289:Pyruvic Acid; D000093:Acetoin; D000095:Acetolactate Synthase; D002262:Carboxy-Lyases; C023746:acetolactate decarboxylase; D007930:Leucine; D014633:Valine