Hydrophobin fusions for high-level transient protein production and purification in Nicotiana benthamiana

Insufficient accumulation levels and the lack of efficient purification methods often prevent the economical production of recombinant proteins in plants. Hydrophobins are small proteins derived from filamentous fungi that are capable of altering the hydrophobicity of their respective fusion partner to enable purification by detergent-based aqueous two-phase separation. In this study, the hydrophobin 1 (HFB1) sequence from Trichoderma reesei was fused to the C-terminus of green fluorescent protein (GFP) and expressed transiently in Nicotiana benthamiana plants by Agrobacterium-infiltration. Interestingly, it was found that the HFB1-fusion significantly enhanced the GFP expression. The GFP-HFB1 construct delayed necrosis of the infiltrated leaves with the concentration of the fusion protein reaching 54% of total soluble protein without the use of viral replication. We are also trying to understand how HFB1-fusions enhance the accumulation of recombinant proteins in plants. It was found that GFP-HFB1 fusions targeted to endoplasmic reticulum form large protein bodies. The packing of HFB1-fusions into these protein bodies may exclude the recombinant protein from normal physiological turnover. A simple and scalable detergent-based aqueous two-phase system was used to purify the HFB1 fusion proteins from plant extracts. The implications of these results for the production of recombinant proteins in plants will be discussed.