Team:TECHNION-ISRAEL/Design

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Modular Tri-Display plasmid






A system capable of displaying various epitopes on the surface of mammalian cells is crucial for inducing immune tolerance. To that end, we have designed a modular display vector capable of displaying up to three different proteins on the membrane of mammalian cells in equimolar ratios.

Our display mechanism is composed of the following parts (Figure 1) (click on them for more information):


igk 2a tag pdgfr epitope 2a

Figure 1: original Tri-Display



To induce immune tolerance, and prevent different allergies and autoimmune diseases, we found the specific sequences that correspond to the epitopes that have been shown to trigger improper immune responses. After we identified the desired epitopes, we ordered them as short single stranded DNA oligomers, combined them to create double stranded DNA, and integrated them into our modular Tri-Display plasmid.

We tested our construct using HSC model. The results of this experiment were less than spectacular. We successfully expressed all three proteins on the membrane, but unfortunately only one protein was expressed significantly. This was both disparaging and confusing. The P2A system is often hailed as having close to 100% cleavage efficiency. [2] As such, we expected to see equal expression of all the proteins, or no expression at all. After extensive research, we discovered the staggering complexity and variability of 2A systems. Most importantly we discovered that 2A peptides followed by a secretory signal sequences, such as the Igκ leader we were using, often had very low cleavage efficiency. As time was running out, we used the most recent papers published on 2A systems and display mechanisms [4] [5] [6] [7] for guidance in crafting four new, and optimized, Tri-Display vectors. Each of these constructs was carefully designed according to a different strategy. Additionally, the protein order within each construct was randomized to ensure the issue was not caused by specific proteins. In Figure 2 you can see all the different variations of the display mechanism.









Figure 2: Optimized Tri-Display constructs


We primarily focused on replacing the original P2A with the reportedly more efficient T2A, and on creating spacers between our signal sequence and the cleavage points. Additionally, we attempted to use the Secrecon signal sequence, a synthetic sequence with far greater secretion capacity. We tested these four constructs in HSC model and discovered that the T2A sequence had a far lower cleavage efficiency than the original P2A. Fortunately, combining both signal sequences (P2A-T2A construct) lead to significant expression of all three proteins. Expression was not perfectly equimolar, and there is certainly room for further optimization, but for the purpose of inducing immune tolerance, we believe this expression rate is sufficient. [8]

Future plans:

We believe the modular Tri-Display plasmid we created is a versatile and valuable tool. The usage of mammalian membrane display in research and therapeutics is very promising, but The need for the expression, and display, of multiple proteins is a recurring problem [9] that has heretofore not been addressed in mammalian cells. To the best of our knowledge, this construct is the first of its kind, allowing for simultaneous and, nearly equimolar, display of up to three different proteins all within a single modular plasmid. In the future we would like to optimize this plasmid further, attempting to achieve greater, and more uniform, expression of all three proteins.




  1. PDisplay Mammalian Expression Vector - Thermo Fisher Scientific, www.thermofisher.com/order/catalog/product/V66020.
  2. Kim, Jin Hee, et al. "High cleavage efficiency of a 2A peptide derived from porcine teschovirus-1 in human cell lines, zebrafish and mice." PloS one 6.4 (2011): e18556.
  3. de Felipe, Pablo, et al. "Inhibition of 2A-mediated ‘cleavage’of certain artificial polyproteins bearing N‐terminal signal sequences." Biotechnology Journal 5.2 (2010): 213-223.
  4. Yan, Jun, et al. "Signal sequence is still required in genes downstream of “autocleaving” 2A peptide for secretary or membrane-anchored expression." Analytical biochemistry 399.1 (2010): 144-146.
  5. Szymczak-Workman, Andrea L., Kate M. Vignali, and Dario AA Vignali. "Design and construction of 2A peptide-linked multicistronic vectors." Cold Spring Harbor Protocols 2012.2 (2012): pdb-ip067876.
  6. Barash, Steve, Wei Wang, and Yanggu Shi. "Human secretory signal peptide description by hidden Markov model and generation of a strong artificial signal peptide for secreted protein expression." Biochemical and biophysical research communications 294.4 (2002): 835-842.
  7. Minskaia, Ekaterina, and Martin D. Ryan. "Protein coexpression using FMDV 2A: effect of “linker” residues." BioMed research international 2013 (2013).
  8. Baranyi, U., et al. "Persistent molecular microchimerism induces long‐term tolerance towards a clinically relevant respiratory allergen." Clinical & Experimental Allergy 42.8 (2012): 1282-1292.
  9. Korepanova, Alla, et al. "Cloning and expression of multiple integral membrane proteins from Mycobacterium tuberculosis in Escherichia coli." Protein Science 14.1 (2005): 148-158.
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Department of Biotechnology & Food Engineering
Technion – Israel Institute of Technology
Haifa 32000, Israel

    • igem.technion.2017@gmail.com