Improved glycoform-based biopharmaceutical production in plants

Most pharmaceutical proteins are derived not from their natural sources but from recombinant sources synthesized in various expression systems. Plant expression systems, unlike mammalian cell cultures, combine simplicity and low cost of prokaryotic systems and the ability for post-translational modifications inherent in eukaryotes. More than 50% of all human proteins and more than 40% of the currently used pharmaceutical proteins are glycosylated, that is, they are glycoproteins, and their biological activity, pharmacokinetics, and immunogenicity depend on the correct glycosylation pattern(s). The main current strategies of glycoengineering of plant expression systems aimed at obtaining fully humanized proteins for pharmaceutical application are currently being developed, primarily in small biotech companies both in the UK and Canada. This project seeks to develop a collaborative research project with researchers at Plantform, a Canadian biotech company. Plantform is currently developing and exploiting its proprietary expression technology, vivoXPRESS, which uses fast-growing tobacco plants (Nicotiana benthamiana) to produce a wide range of biologic (large molecule) drugs, including monoclonal antibodies and therapeutic proteins. This project will focus on an important glycan processing component of plants, the STT3 a subunit of the oligosaccharyltransferase complex of the ER lumen. In particular Plantform are interested in understanding the molecular basis for STT3 function in the context of their expression platform. The project will entail the recombinant expression of the leishmania STT3 subunit in plants, which is used to increase the extent of glycosylation in the leaf-based systems. The student will then purify the protein and determine its structure using single particle cryo-EM. The structure will be used to make specific mutations and their effect on glycosylation in the plant system analysed using HPLC and mass spectrometry.