Optimization of recombinant maize CDKA;1 and CycD6;1 production in Escherichia coli by response surface methodology

The complex formed by the cyclin-dependent kinase A (CDKA) and cyclin D is responsible for the G1-S transition in the plant cell cycle. Maize (Zea mays L) CDKA; 1 and CycD6; 1 were cloned and expressed in E. coli. The present study describes the optimization of both proteins production using a statistical approach known as response surface methodology (RSM). The experimental design took into account the effects of four variables: optical density of the culture (OD₆₀₀) before induction, isopropyl β-d-1-thiogalactopyranoside (IPTG) concentration, post-induction temperature, and post-induction time. For each protein, a 2⁴ full factorial central composite rotary design for these four independent variables (at five levels each) was employed to fit a polynomial model; which indicated that 30 experiments were required for this procedure. An optimization of CDKA; 1 and CycD6; 1 production levels in the soluble fraction was achieved. Protein conformation and stability were studied by circular dichroism and fluorescence spectroscopy. Finally, in vitro Cyc-CDK complex formation and its kinase activity were confirmed.