DIRECTED EVOLUTION OF BIOSYNTHETIC PATHWAYS - RECRUITMENT OF CYSTEINETHIOETHERS FOR CONSTRUCTING THE CELL-WALL OF ESCHERICHIA-COLI

We report that expansion of thioether biosynthesis in Escherichia coli generates sulfur-containing amino acids that can replace meso-diamino pimelate, the essential amino acid used for cross-linking the cell wal l. This was accomplished by jointly overexpressing the metB gene codin g for L-cystathionine gamma-synthase and disrupting the metC gene, who se product, L-cystathionine beta-lyase, is responsible for the destruc tion of L-cystathionine and other L-cysteine thioethers. As a result, meso-lanthionine and L-allo-cystathionine were produced endogenously a nd 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 ch emical constitution of living cells beyond its present state.