title: Identification and characterization of two new 5-keto-4-deoxy-D-Glucarate Dehydratases/Decarboxylases.
abstract: 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.
  
  
  
  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 Km, kcatand 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 Km1.0 mM, kcat4.5 s-1, for C. testosteroni Km1.1 mM, kcat3.1 s-1, and for P. naphthalenivorans Km1.1 mM, kcat1.7 s-1. The two new enzymes had a slightly lower catalytic activity (increased Kmand a decreased kcat) 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.
  
  
  
  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.
authors.affiliation: Technical University of Munich, Straubing Center of Science, Chair of Chemistry of Biogenic Resources, Schulgasse 16, 94315, Straubing, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Pick
authors.affiliation: Technical University of Munich, Straubing Center of Science, Chair of Chemistry of Biogenic Resources, Schulgasse 16, 94315, Straubing, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Beer
authors.affiliation: Department of Biosciences and Informatics, Keio University, 3-14-1 Hiyoshi, 2238522, Yokohama, Japan.
authors.forename: Risa
authors.initials: R
authors.lastname: Hemmi
authors.affiliation: Department of Biosciences and Informatics, Keio University, 3-14-1 Hiyoshi, 2238522, Yokohama, Japan.
authors.forename: Rena
authors.initials: R
authors.lastname: Momma
authors.affiliation: Technical University of Munich, Straubing Center of Science, Chair of Chemistry of Biogenic Resources, Schulgasse 16, 94315, Straubing, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Schmid
authors.affiliation: Department of Biosciences and Informatics, Keio University, 3-14-1 Hiyoshi, 2238522, Yokohama, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Miyamoto
authors.affiliation: Technical University of Munich, Straubing Center of Science, Chair of Chemistry of Biogenic Resources, Schulgasse 16, 94315, Straubing, Germany. sieber@tum.de.
authors.forename: Volker
authors.initials: V
authors.lastname: Sieber
mesh_terms: D020562:Betaproteobacteria / Q000201:enzymology*; D001665:Binding Sites; D020604:Comamonas testosteroni / Q000201:enzymology*; D004789:Enzyme Activation; D004795:Enzyme Stability; D005977:Glutarates / Q000737:chemistry*; D006836:Hydro-Lyases / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D013379:Substrate Specificity
chemical_list: D005977:Glutarates; D006836:Hydro-Lyases; C020572:glucarate dehydratase
keywords: Acinetobacter baylyi; Comamonas testosteroni; Dehydratase; Keto-deoxy-D-Glucarate; Polaromonas naphthalenivorans