Characterization of recombinant dihydrodipicolinate synthase from the bread wheat Triticum aestivum.

Abstract

Recombinant wheat DHDPS was produced for the first time in milligram quantities and shown to be an enzymatically active tetramer in solution using analytical ultracentrifugation and small angle X-ray scattering. Wheat is an important cereal crop with an extensive role in global food supply. Given our rapidly growing population, strategies to increase the nutritional value and production of bread wheat are of major significance in agricultural science to satisfy our dietary requirements. Lysine is one of the most limiting essential amino acids in wheat, thus, a thorough understanding of lysine biosynthesis is of upmost importance to improve its nutritional value. Dihydrodipicolinate synthase (DHDPS; EC 4.3.3.7) catalyzes the first committed step in the lysine biosynthesis pathway of plants. Here, we report for the first time the expression and purification of recombinant DHDPS from the bread wheat Triticum aestivum (Ta-DHDPS). The optimized protocol yielded 36mg of > 98% pure recombinant Ta-DHDPS per liter of culture. Enzyme kinetic studies demonstrate that the recombinant Ta-DHDPS has a KM (pyruvate) of 0.45mM, KM (l-aspartate-4-semialdehyde) of 0.07mM, kcat of 56s-1, and is inhibited by lysine (IC 50 LYS of 0.033mM), which agree well with previous studies using labor-intensive purification from wheat suspension cultures. We subsequently employed circular dichroism spectroscopy, analytical ultracentrifugation and small angle X-ray scattering to show that the recombinant enzyme is folded with 60% α/β structure and exists as a 7.5S tetrameric species with a Rg of 33Å and Dmax of 118Å. This study is the first to report the biophysical properties of the recombinant Ta-DHDPS in aqueous solution and offers an excellent platform for future studies aimed at improving nutritional value and primary production of bread wheat.