Expression of recombinant proteins in mammalian cells
The production of a protein with a high-quality and high-quantity is a requirement at any time, and there is a gradual increase in the use of mammalian cells for protein production. Mammalian cells are the natural source of many therapeutic proteins and are used as the best system for the production of recombinant proteins with clinical application.
These expression systems are capable of properly recombinant protein folding, making post-translational changes, including glycosylation, signal peptide processing, protein secretion, and endotoxin-free. It can also be used to transient or sustained expression.
Despite the great benefits of this system, the stable cell lines of the mammals are obtained only after a long period, and after the construction of the cell line, cells are required to be continuously maintained under selective pressure, and they may become unstable upon long-term culturing.
Possible contamination with animal viruses in the mammalian expression system is another limitation in their use for mass production. On the other hand, most of the inductive promoters in these systems exhibit a level of continuous activity. Human recombinant proteins are often expressed in mouse cell lines, so recombinant protein has a rat glycosylation pattern. Although these cell lines can have -N glycans similar to humans, the Galα1-3Gal non-branched carbohydrate group is added to the recombinant protein produced in these cell lines, which this carbohydrate group is not found in the in human proteins. On the other hand, human proteins produced in mouse cells exhibit a different composition of sialic acid. Other problems of mammalian expression systems are including low levels of recombinant protein production, slow growth, and instability.