Many important pharmaceutical proteins, such as antibodies and insulin, are derived from mammalian organisms. These cells have an organelle called the endoplasmic reticulum that creates an isolated environment for proteins to fold correctly and form disulfide bonds. Yet, mammalian cells can be difficult to grow and are not ideal for industrial production of pharmaceutical proteins. Fast growing organisms such as E.coli provide us with the advantage of producing and purifying large amounts of protein in a short amount of time. However, prokaryotes don’t contain endoplasmic reticulums, making it challenging to properly fold pharmaceutical proteins.

Disulfide bonds occur naturally in E.coli in the periplasm, the space between the inner and outer membranes of the bacteria. The oxidizing environment of the periplasm is similar to the endoplasmic reticulum and allows disulfide bond formation. Indeed, funneling a mammalian protein through the periplasm of an E.coli cell allows for proper folding and disulfide bonding.

Additionally, the production of antibodies have become paramount in biotechnology and medicine. As you can see in Table 1, of the top 10 drugs with the highest grossing sales in 2014, three of the drugs are comprised of purified monoclonal antibody therapies. Antibody therapies remain difficult to produce and purify, and thus improvements on the purification process are greatly needed to continue to produce these drugs efficiently.

In our project, we've created a construct capable of purifying antibody fragments by tagging a bacterial secretion protein, OsmY, to an antibody scFv (single chain fragment variable) and over-expressing the construct in E.coli. To demonstrate the importance of our study we've chosen to produce an antibody specific to Dihydroxy acid Dehydradatase (DADH), a Salmonella protein. Salmonella infections are responsible for 23,000 hospitalizations in the US each year, highlighting the need for large quantities of inexpensive sensors and treatments. To further demonstrate the value of our part we've compared our secretion system with industrially used secretion system that use the secretion tag pelB.