Identification and characterization of two new 5-keto-4-deoxy-D-Glucarate Dehydratases/Decarboxylases.

BACKGROUND: Hexuronic acids such as D-galacturonic acid and D-glucuronic acid can be utilized via different pathways within the metabolism of microorganisms. One representative, the oxidative pathway, generates α-keto-glutarate as the direct link entering towards the citric acid cycle. The penultimate enzyme, keto-deoxy glucarate dehydratase/decarboxylase, catalyses the dehydration and decarboxylation of keto-deoxy glucarate to α-keto-glutarate semialdehyde. This enzymatic reaction can be tracked continuously by applying a pH-shift assay. RESULTS: Two new keto-deoxy glucarate dehydratases/decarboxylases (EC 4.2.1.41) from Comamonas testosteroni KF-1 and Polaromonas naphthalenivorans CJ2 were identified and expressed in an active form using Escherichia coli ArcticExpress(DE3). Subsequent characterization concerning K m, k cat and thermal stability was conducted in comparison with the known keto-deoxy glucarate dehydratase/decarboxylase from Acinetobacter baylyi ADP1. The kinetic constants determined for A. baylyi were K m 1.0 mM, k cat 4.5 s-1, for C. testosteroni K m 1.1 mM, k cat 3.1 s-1, and for P. naphthalenivorans K m 1.1 mM, k cat 1.7 s-1. The two new enzymes had a slightly lower catalytic activity (increased K m and a decreased k cat) but showed a higher thermal stability than that of A. baylyi. The developed pH-shift assay, using potassium phosphate and bromothymol blue as the pH indicator, enables a direct measurement. The use of crude extracts did not interfere with the assay and was tested for wild-type landscapes for all three enzymes. CONCLUSIONS: By establishing a pH-shift assay, an easy measurement method for keto-deoxy glucarate dehydratase/decarboxylase could be developed. It can be used for measurements of the purified enzymes or using crude extracts. Therefore, it is especially suitable as the method of choice within an engineering approach for further optimization of these enzymes.

Draft Genome Sequence of Bordetella bronchiseptica KU1201, the First Isolation Source of Arylmalonate Decarboxylase.

The analysis of the 6.8-Mbp draft genome sequence of the phenylmalonate-assimilating bacterium Bordetella bronchiseptica KU1201 identified 6,358 protein-coding sequences. This will give us an insight into the catabolic variability of this strain for aromatic compounds, along with the roles of arylmalonate decarboxylases in nature.