Process engineering strategy for recombinant protein recovery from canola by cation exchange chromatography

The suitability of canola as a recombinant protein production host was evaluated in terms of the potential for simple chromatographic recovery by ion exchange. To investigate the influence of the charge of a recombinant protein on recovery from canola, a series of mutants of T4 lysozyme of varying charge were used to model the situation of transgenic expression by being spiked into nontransgenic canola protein extracts. This mixture was then fractionated by cation exchange chromatography. Two different means of charge modification were compared, namely, point mutations and fusions. Point mutations proved the better means for adding positive charges. A linear relationship between the protein charge and the eluent conductivity, which could be used to guide the genetic engineering for protein recovery from canola, was found. It showed that an increase of +1 charge on T4 lysozyme increased the required conductivity (molarity) of the eluent by 0.068 mS/cm (27.8 mM NaCl). For this specific case, T4 lysozyme with a nominal charge of +7 moves the point of elution into a valley between two major native canola protein peaks, where substantial one-step enrichment can be obtained. Equivalent charge changes provided by polyarginine fusions gave very wide elution patterns that were ascribed to either proteolytic degradation within the polyarginine fusion or interaction of the polyarginine with polyanions present in canola. While the above results came after a dialysis step to adjust the canola extract, elimination of the dialysis step did not significantly influence the purification behavior of the cation-exchange column. However, a more severe resin regeneration scheme was needed to maintain the column's performance.