Big Potential in Using Protozoans for Producing Mammalian Proteins

Recombinant protein expression is critical for functionally studying proteins, preparing antigens, providing tissue culture growth supplement, and producing certain therapeutic compounds. Like many molecular biology labs, we have used several heterologous protein expression systems over the last decade including E. coli, yeasts, insect cells and mammalian cells from various species. It is widely accepted that these systems present increasing functional relevance from bacteria to mammalian cells, with accompanying increase in difficulty and cost. The benefits of using cells from higher species are often reflected in post-translational modifications (PTMs), such as glycosylation, phosphorylation, etc.

There is yet another system that could be easy to handle while maintaining mammalian-like PTMs–parasitic protozoan Leishmania tarentolae. L. tarenolae is a unicellular organism, its host is lizard. Even though it’s a vertebrate parasite, this species poses no risk to humans. Amazingly, L. tarenolae individuals can be grown on agar plates for clonal selection or in simple liquid media like E. coli. Their optimal growth temperature is 27C, and they do not require shaking; thus they are suitable for growth in insect cell incubators or even at room temperature. The most important advantage of this system is that oligosaccharide structures of proteins produced in this organism resemble those of mammalian cells much more closely than even insect cells, i. e. the N-glycosylation profile can be basically identical to a biantennary fully galactosylated Man3GlcNAc2core-a-1,6-fucosylated structure found in mammalian cells.

IFrom our first-hand experience, the handling of this species is extremely convenient. While we heavily promote the baculovirus expression system (BVES) for most of our custom protein production projects (we carried out one NIH project for producing human glycosylated cancer antigen proteins using a modified BVES recently), we now believe that there is a good chance that many of the proteins we have been producing could be produced in the protozoan system with potentially better efficiency.

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