Functional and biochemical characterization of a recombinant Arabidopsis thaliana 3-deoxy-D-manno-octulasonate 8-phosphate synthase

摘要

An open reading frame, encoding for KDOPS (3-deoxy-D-manno-octulosonate 8-phosphate synthase), from Arabidopsis thaliana was cloned into a T7-driven expression vector. The protein was overexpressed in Escherichia coli and purified to homogeneity. Recombinant A. thaliana KDOPS, in solution, displays an apparent molecular mass of 76 kDa and a subunit molecular mass of 31.519 kDa. Unlike previously studied bacterial KDOPSs, which are tetrameric, A. thaliana KDOPS appears to be a dimer in solution. The optimum temperature of the enzyme is 65 degreesC and the optimum pH is 7.5, with a broad peak between pH 6.5 and 9.5 showing 90% of maximum activity. The enzyme cannot be inactivated by EDTA or dipicolinic acid treatment, nor it can be activated by a series of bivalent metal ions, suggesting that it is a non-metal to-enzyme, as opposed to the initial prediction that it would be a metallo-enzyme. Kinetic studies showed that the enzyme follows a sequential mechanism with K-m = 3.6 muM for phosphoenolpyruvate and 3.8 muM for D-arabinose 5-phosphate and k(cat) = 5.9 s(-1) at 37 degreesC. On the basis of the characterization of A. thaliana KDOPS and phylogenetic analysis, plant KDOPSs may represent a new, distinct class of KDOPSs.