Clavulanic acid biosynthesis; the final steps

Abstract

The chemically unstable anabolite (3R,5R)-clavulanate-9-aldehyde 1 and an NADPH dependent dehydrogenase have been detected in the broth of Streptomyces clavuligerus. The purified enzyme was shown to make clavulanic acid by reduction of the aldehydic moiety of synthetic 1 to the allylic alcohol of clavulanic acid 2. A DNA sequence corresponding to the enzyme’s N-terminal amino acid sequence was located within the clavulanic acid biosynthetic gene cluster. We have named this novel enzyme clavulanic acid dehydrogenase (CAD). In an attempt to determine the origin of 1, fermentations of S. clavuligerus were fed ornithine labelled with stable isotopes in the carboxy group. The results of these experiments are discussed.