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J. Bacteriol., Jun 1996, 3015-3024, Vol 178, No. 11
ZL Boynton, GN Bennet and FB Rudolph
The enzymes beta-hydroxybutyryl-coenzyme A (CoA) dehydrogenase (BHBD),
crotonase, and butyryl-CoA dehydrogenase (BCD) from Clostridium
acetobutylicum are responsible for the formation of butyryl-CoA from
acetoacetyl-CoA. These enzymes are essential to both acid formation and
solvent formation by clostridia. Clustered genes encoding BHBD, crotonase,
BCD, and putative electron transfer flavoprotein alpha and beta subunits
have been cloned and sequenced. The nucleotide sequence of the crt gene
indicates that it encodes crotonase, a protein with 261 amino acid residues
and a calculated molecular mass of 28.2 kDa; the hbd gene encodes BHBD,
with 282 residues and a molecular mass of 30.5 kDa. Three open reading
frames (bcd, etfB, and etfA) are located between crt and hbd. The
nucleotide sequence of bcd indicates that it encodes BCD, which consists of
379 amino acid residues and has high levels of homology with various
acyl-CoA dehydrogenases. Open reading frames etfB and etfA, located
downstream of bcd, encode 27.2- and 36.1- kDa proteins, respectively, and
show homology with the fixAB genes and the alpha and beta subunits of the
electron transfer flavoprotein. These findings suggest that BCD in
clostridia might interact with the electron transfer flavoprotein in its
redox function. Primer extension analysis identified a promoter consensus
sequence upstream of the crt gene, suggesting that the clustered genes are
transcribed as a transcriptional unit and form a BCS (butyryl-CoA
synthesis) operon. A DNA fragment containing the entire BCS operon was
subcloned into an Escherichia coli-C. acetobutylicum shuttle vector. Enzyme
activity assays showed that crotonase and BHBD were highly overproduced in
cell extracts from E. coli harboring the subclone. In C. acetobutylicum
harboring the subclone, the activities of the enzymes crotonase, BHBD, and
BCD were elevated.
Copyright © 1996, American Society for Microbiology
Cloning, sequencing, and expression of clustered genes encoding beta- hydroxybutyryl-coenzyme A (CoA) dehydrogenase, crotonase, and butyryl- CoA dehydrogenase from Clostridium acetobutylicum ATCC 824
Department of Biochemistry and Cell Biology, The Institute of Biosciences and Bioengineering, Rice University, Houston, Texas 77005- 1892, USA.
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