Improving Recombinant Protein Recovery from Plant Tissue Using Heat Precipitation

Plants are increasingly viewed as suitable expression hosts for the production of recombinant proteins, especially when oxidative folding and/or posttranslational modification is essential for protein stability and functionality. In contrast to traditional platforms such as yeast and mammalian cells, where the product is secreted into the culture medium, recombinant proteins expressed in plants are usually retained within the cells so additional effort is required during extraction and purification. Various extraction processes are used to release soluble proteins from plant tissues, followed by clarification to remove fibers and particulates before the target protein is purified. Fermentation media generally contain few proteins, making it easier to recover a secreted product, whereas the green juice extracted from plants usually contains a large number of host proteins that interfere with target isolation and purification. In this chapter, we describe the use of heat precipitation to remove a large portion of the host cell proteins, thus improving the efficiency of subsequent purification steps and the quality of the purified recombinant protein.