The mde operon and an upstream regulatory gene (mdeR) have been cloned and sequenced from Pseudomonas putida chromosomal DNA. The mde operon contains two structural genes involved in L-methionine degradative metabolism, which are mdeA (L-methionine γ-lyase gene) and mdeB (a gene encoding a homologous protein to the E1 component of pyruvate dehydrogenase complex). A rho-independent terminator was present just downstream of mdeB and open reading frames corresponding to other components of α-keto acid dehydrogenase complex were not found. When the mdeB gene product was overproduced in Escherichia coli, the E1 activity of the cell extract showed high specificity for α-ketobutyrate rather than pyruvate. these results suggest that mdeB encodes a novel E1 component, α-ketobutyrate dehydrogenase E1 component, and plays an important role in the metabolism of α-ketobutyrate produced by L-methionine γ-lyase from L-methionine. In addition,we found that mdeR gene was located on the opposite strand and began at 127 bp from the translational start site of mdeA. The mdeR gene product has been idetified as a member of the leucine responsive regulatory protein (Lrp) family and revealed to act as an essential positive regulator allowing the expression of the mdeAB operon.
L-methionine
α-ketobutyrate
mde operon
pyruvate dehydrogenase E1 component
leucine responsive regulatory protein