The glycyl radical enzyme TdcE can replace pyruvate formate-lyase in glucose fermentation.
Mutants of Escherichia coli unable to synthesize a functional pyruvate formate-lyase (PFL) are severely impaired in their capacity to grow by glucose fermentation. In a functional complementation assay designed to isolate the pfl gene from Clostridium butyricum, we fortuitously identified a gene that did not encode a PFL but nonetheless was able to complement the phenotypic defects caused by an E. coli pfl mutation. The clostridial gene encoded a basic 14. 5-kDa protein (TcbC) which, based on amino acid similarity and analysis of immediately adjacent DNA sequences, was part of a transposase exhibiting extensive similarity to the product of the site-specific transposon Tn554 from Staphylococcus aureus. Our studies revealed that the clostridial TcbC protein activated the transcription of the E. coli tdcABCDEFG operon, which encodes an anaerobic L-threonine-degradative pathway. Normally, anaerobic synthesis of the pathway is optimal when E. coli grows in the absence of catabolite-repressing sugars and in the presence of L-threonine. Although anaerobic control of pathway synthesis was maintained, TcbC alleviated glucose repression. One of the products encoded by the tdc operon, TdcE, has recently been shown to be a 2-keto acid formate-lyase (C. Hesslinger, S. A. Fairhurst, and G. Sawers, Mol. Microbiol. 27:477-492, 1998) that can accept pyruvate as an enzyme substrate. Here we show that TdcE is directly responsible for the restoration of fermentative growth to pfl mutants.
Sawers
G
G
Nitrogen Fixation Laboratory, John Innes Centre, Norwich, United Kingdom. gary.sawers@bbsrc.ac.uk
Hesslinger
C
C
Muller
N
N
Kaiser
M
M
D000123:Acetyltransferases / Q000378:metabolism*; D000217:Acyltransferases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D005285:Fermentation; D017353:Gene Deletion; D005947:Glucose / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010641:Phenotype; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D000217:Acyltransferases; D000123:Acetyltransferases; C111105:tdcE protein, E coli; C022560:formate C-acetyltransferase; D005947:Glucose; D010100:Oxygen