The production of recombinant proteins involves the transfection of cells with the desired gene into a DNA vector. The gene is then converted into a protein using the host cell's machinery. This expressed protein can then be extracted by cell lysis and subsequent purification steps. Prokaryotic and eukaryotic expression systems are widely used. Each system has its own advantages. A particular mammalian recombinant protein expression system is selected depending on economic and qualitative aspects such as protein type, function and desired protein yield.
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Expression systems for bacteria, yeast, insects, and mammals are widely used. Recently, researchers have also used cellular expression systems.
Bacterial expression system
They offer large-scale recombinant protein production in a short period of time (E. coli doubling time is 20 minutes). It requires simple (moderate, additive) cultivation conditions that are scalable and inexpensive. Disadvantages of this system include difficulty in expressing certain mammalian proteins, accumulation of proteins such as inclusion bodies, contamination by protease proteins from host proteins resulting in degradation of expressed proteins, and accumulation of endotoxins. e.g. Escherichia coli, Bacillus subtilis.
Yeast expression system
A well-defined and economical system of eukaryotic expression. It combines the advantages of prokaryotic and eukaryotic expression systems. This system is used to express secretory as well as intracellular proteins. This system offers high protein yield, post-translational modifications, less expression time, and requires a simple environment. This system can be optimized for high protein expression (grams) with the help of a fermenter.