Recombinant E. coli metC protein (a.a. 1-392) [His]

We report that expansion of thioether biosynthesis in Escherichia coli generates sulfur-containing amino acids that can replace meso-diaminopimelate, the essential amino acid used for cross-linking the cell wall. This was accomplished by jointly overexpressing the metB gene coding for L-cystathionine gamma-synthase and disrupting the metC gene, whose product, L-cystathionine beta-lyase, is responsible for the destruction of L-cystathionine and other L-cysteine thioethers. As a result, meso-lanthionine and L-allo-cystathionine were produced endogenously and incorporated in the peptidoglycan, thereby enabling E. coli strains auxotrophic for diaminopimelate to grow in its absence. Thus, current techniques of metabolic engineering can be applied to evolving the chemical constitution of living cells beyond its present state.

In Escherichia coli, the enzyme called cysteine desulfhydrase (CD), which is responsible for L-cysteine degradation, was investigated by native-PAGE and CD activity staining of crude cell extracts. Analyses with gene-disrupted mutants showed that CD activity resulted from two enzymes: tryptophanase (TNase) encoded by tnaA and cystathionine P-lyase (CBL) encoded by metC. It was also found that TNase synthesis was induced by the presence Of L-Cysteine. The tnaA and metC mutants transformed with the plasmid containing the gene for feedback-insensitive serine acetyltransferase exhibited higher L-Cysteine productivity than the wild-type strain carrying the same plasmid. These results indicated that TNase and CBL did act on L-Cysteine degradation in E. coli cells.