Improvement of glycosyltransferases for in vitro glycan remodeling of plant derived therapeutic proteins.

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Plants represent an excellent cost-effective alternative to mammalian cell culture for production of protein based drugs known as biologics. These drugs are proteins derived from normal human biology, where they protect us from various natural and man-made toxins, infectious disease, and immune system malfunctions like cancer. These are produced as recombinant proteins and are very expensive to manufacture in tissue culture. Normal human therapeutic proteins are decorated with molecules called glycans making them "glycoproteins", and these glycans are essential for stability and longevity in the body. The biochemical machinery for making glycoproteins in plants and animals is almost identical, resulting in plants being able to make some important human proteins, like antibodies, and proteins which protect from toxins like nerve gas. Plants however don't naturally make human style glycan decorations on plants, and plant glycans can cause an allergic reaction. Recent advances in plant engineering now allows researchers to produce proteins without the plant specific decorations which make the proteins a target of the human immune system. However, the production of the authentic human glycan decorations is still difficult to control in both mammalian- and plant-based expression systems. PlantForm, and the Wakarchuk lab are collaborating to use enzymes in the laboratory to finish the glycan decorations exactly as those found on the normal human protein with the goal of commercial-scale glycan modification of target proteins. To this end, the enzymes required to change the glycans are being engineered for improved production, activity and stability through our unique bacterial expression systems. We are developing immobilized enzymes to produce various terminal glycan decorations such that the proteins don't require extensive re-purification after the reactions. We are also engineering production of these enzymes in a bacterium which doesn't produce a toxic contaminant - endotoxin - which requires significant effort to remove from these high value proteins.