Building on what nature gave us: Engineering cell glycosylation pathways

Recombinant protein production is currently a multibillion dollar industry and, although it isprojected to continue to grow rapidly, faces several significant challenges to reach its fullpotential. One of these challenges lies in the production of proteins with 'human' posttranslationalmodifications (PTM) using the bacterial, fungal, and rodent cell lines widelyused in the biotechnology industry. The need for appropriate PTM is exemplified byglycosylation, the process by which glycans are added to the cell surface and secretedproteins, which is a critical determinant of biological activity and pharmacological properties.This chapter provides an overview of recent strategies used in the development of large-scale,cost-effective production and manufacturing processes of biologically synthesizedglycoproteins. To date, these strategies have included both the metabolic engineering of thehost cell's enzymes responsible for glycosylation as well as the supplementation of theendogenous 'glycosylation machinery' with foreign genes. Once a re-engineeredglycosylation pathway has been installed into a host cell, or living organisms including plants,birds, or livestock, the requirement for adequate metabolic intermediates to provide sufficientflux through the pathway to ensure high product quality must be met; therefore this chapterwill also discuss strategies used to supply these intermediates in cells used as hosts forglycoprotein production. Finally, the chapter concludes with a discussion of 'metabolicoligosaccharide engineering' methods where non-natural metabolic intermediates areincorporated into glycosylation pathways thereby endowing glycoproteins with novelproperties not found in nature.