Ask A Bioprocess Consultant: What Are Recombinant Proteins?
Recombinant proteins are a type of modified protein whose amino acid sequence is encoded by recombinant DNA which has been cloned into an expression vector and expressed through host such as bacteria, yeast or mammalian cells.
- The technology surrounding recombinant protein expression is possible because of the similarity that exists in almost all genetic material of living organisms, that being comparable DNA nucleotides between all living organisms – adenine, thymine, guanine and cytosine.
- Selection of an expression host is usually based on the complexity of recombinant protein being expressed and its intended use. Bacteria are typically used to express simpler recombinant proteins that have little to no post-translational modifications. In contrast, mammalian cells are used when specific or complex post-translational modifications are required, such as glycosolation, deamidation, methylation, etc. Between these two extremes exists yeast expression systems which allow for some simple post-translational modifications of the expressed recombinant protein.
How Are Recombinant Proteins Made?
Once a recombinant protein sequence is known, and a cell line capable of producing the target is established, a development program is pursued that focuses on the specific conditions required to propagate the recombinant protein of interest to high levels. Typically, there is a focus on the upstream preculture and production culture conditions where the host cells are grown to a high density. The recombinant proteins can either be produced by the cells constitutively, meaning that the cells are always producing the recombinant protein during their life cycle, or through induction where the culture is induced to ‘turn on’ recombinant protein expression by the hosts cellular machinery.
In either case, the combination of cell density and specific cell productivity are the main driving factors of producing high titers of recombinant proteins. With the upstream process producing the recombinant protein of interest at acceptable titers, the next challenge is harvesting to recover the recombinant proteins from the culture so that it can be further purified into a highly pure formulation acceptable for delivery to human patients. Harvest operations are dictated by where the recombinant protein is expressed. For recombinant proteins that are expressed intracellularly, the cells must be opened through mechanical disruption to free the recombinant protein of interest for further purification, while extracellular expression (secretion) allows for the simple separation of the cells from the recombinant proteins through depth filtration.
Coming out of harvest the recombinant protein are contained in a ‘soup’ of culture contaminants containing all sorts of proteins, enzymes, genetic material and metabolic by-products that must be separated from the target recombinant protein of interest. This is accomplished through downstream purification operations that typically involve several column chromatography and tangential flow filtration steps that are designed to selectively target and capture the recombinant protein of interest to increase its purity successively. At the end of processing the target recombinant protein ends up highly purified in a formulation that is compatible with both the protein and human physiology, ready to act as a life-saving medicine as a therapeutic, vaccine or diagnostic.
BPAI: Bioprocessing and Biologics Consulting
If you need help from a Bioprocess Consultant with the development and manufacturing of your recombinant protein, please call us at Bio-Processing Alliance (BPAI) to arrange a meeting with our Biologics Consulting experts. Our wealth of experience in the expression, purification and GMP manufacturing of recombinant proteins for human clinical and commercial use can help you advance your important program forward quickly and effectively.