Is plant biotin holocarboxylase synthetase a bifunctional enzyme?
Holocarboxylase synthetases (HCSs) catalyse the biotinylation of biotin-dependent carboxylases in both prokaryotes and eukaryotes. In Escherichia coli and Bacillus subtilis, the protein also acts as a transcriptional repressor that regulates the synthesis of biotin. Previously, we isolated and characterized a cDNA encoding an Arabidopsis thaliana HCS and subsequently assigned this enzyme form to the chloroplast compartment. To investigate whether or not the Arabidopsis protein may function as a regulator in E. coli, we have expressed the functional plant HCS in a birA-derepressed mutant strain of E. coli devoid of the corresponding E. coli protein and carrying a promoter-less LacZ gene marker inserted into the biotin operon, such that the bio promoter drives the synthesis of beta-galactosidase. Our data demonstrate that although the expressed plant HCS efficiently complemented the function of apo-carboxylase biotinylation in E. coli, it proved unable to regulate the expression of the biotin biosynthetic genes.
Alban
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Laboratoire mixte CNRS-Aventis (UMR1932 associée au CNRS), Aventis CropScience, Lyon, France. claude.alban@aventis.com
D017360:Arabidopsis / Q000201:enzymology*; D001710:Biotin / Q000235:genetics; D019731:Carbon-Nitrogen Ligases / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D015870:Gene Expression; D007700:Kinetics; D009876:Operon; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D011994:Recombinant Proteins; D001710:Biotin; D001616:beta-Galactosidase; D019731:Carbon-Nitrogen Ligases; C023312:holocarboxylase synthetases