Purification and characterization of a dual function 3-dehydroquinate dehydratase from Amycolatopsis methanolica
1992
Euverink, G.J.W. | Hessels, G.I. | Vrijbloed, J.W. | Coggins, J.R. | Dijkhuizen, L.
Studies on hydroaromatic metabolism in the actinomycete Amycolatopsis methanolica revealed that the organism grows rapidly on quinate (but not on shikimate) as sole carbon- and energy source. Quinate is initially converted into the shikimate pathway intermediate 3-dehydroquinate by an inducible NAD+-dependent quinate/shikimate dehydrogenase. 3-Dehydroquinate dehydratase subsequently converts 3-dehydroquinate into 3-dehydroshikimate, which is used partly for the biosynthesis of aromatic amino acids, and is partly catabolized via protocatechuate and the beta-ketoadipate pathway. Enzyme studies and analysis of mutants clearly showed that the single 3-dehydroquinate dehydratase present in A. methanolica has a dual function, the first example of a 3-dehydroquinate dehydratase enzyme involved in both the catabolism of quinate and the biosynthesis of aromatic amino acids. This enzyme was purified over 1700-fold to homogeneity. Its further characterization indicated that it is a Type II 3-dehydroquinate dehydratase, a thermostable enzyme with a large oligomeric structure (native Mr 135 X 10(3)) and a subunit Mr of 12 X 10(3). Characterization of aromatic amino acid auxotrophic mutants of A. methanolica suggested that genes encoding 3-dehydroquinate synthase and 3-dehydroquinate dehydratase are genetically linked but their transcription results in the synthesis of two separate proteins.
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