Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5516091 | Protein Expression and Purification | 2017 | 10 Pages |
â¢cis-dihydrodiol naphthalene dehydrogenase (NahB) was overexpressed in E. coli.â¢ligand supplementation was used to stabilize the protein in solution.â¢structural and kinetic analysis of recombinant NahB were performed.â¢fourteen crystallization conditions were obtained for the enzyme.â¢diffraction data at 2.21 A allowed the structure determination of the enzyme.
The second enzyme of the naphthalene degradation pathway in Pseudomonas putida G7 is NahB, a dehydrogenase that converts cis-1,2-dihydroxy-1,2-dihydronaphthalene to 1,2-dihydroxynaphthalene. We report the cloning, optimization of expression, purification, kinetic studies and preliminary structural characterization of the recombinant NahB. The nahB gene was cloned into a T7 expression vector and the enzyme was overexpressed in Escherichia coli Rosetta (DE3) as an N-terminal hexa-histidine-tagged protein (6xHis-NahB). Using methods of enhancing protein stability in solution, we tested different expression, cell lysis, and purification protocols with and without ligand supplementation. The protein stability was evaluated by dynamic light scattering and circular dichroism spectroscopy assays. Best-derived protocols (expression at 18 °C, cell lysis with homogenizer, and three purification steps) were used to produce 20 mg of homogeneous 6xHis-NahB per liter of culture. The secondary and quaternary structures of 6xHis-NahB were assessed by circular dichroism and size-exclusion chromatography experiments, respectively. The enzyme was NAD+-dependent and active at pH 7.0 and 9.4 for the oxidation of the substrate. The Michaelis-Menten parameters determined at pH 7.0 and 25 °C for the substrate and cofactor, presented respective Km values of 6 and 350 μM, and a kcat value of 8.3 sâ1. Furthermore, we identified conditions for the crystallization of 6xHis-NahB. X-ray diffraction data were collected from a single 6xHis-NahB crystal which diffracted to 2.21 à . The crystal belongs to space group I222, with unit-cell parameters a = 63.62, b = 69.50, and c = 117.47 à . The tertiary structure of 6xHis-NahB was determined using the molecular replacement method. Further structural refinement is currently underway.