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Team:Tokyo Tech/Antifreeze
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Contents |
Achievement
- We achieved to introduce AFP derived from mealworm into E.coli strains Origami 2 and confirm the expression of AFP in the strain.
Introduction ~Why do we need Anti-freeze protein(AFP)~
The surface temperature of Mars is below freezing point of water almost all day. Most organisms can not survive in such a severe environment even if we successed to send them to the Mars. However, fish in the Arctic Ocean survive even though the temperature of the sea is below freezing points. They could survive because they have anti-freeze protein. Anti-freeze protein would enable organisms to surbvive in low temperature. Therefore, we tried to introduce Anti-freeze protein(AFP) into bacteria. By producing AFP, bacteria will become surviving in Mars.
Material and Method
The characteristics of Anti-freeze protein(AFP)
Anti-freeze protein(AFP) is defined as a protein that binds to a single ice crystal specifically and inhibits growth of the ice. For that reason AFP is thought to lower the freezing point while havinng no effect on the melting point. This characteristics of AFP is called Thermal Hysteresis (TH), AFP is superior to other substances(such as NaCl), for it can greatly lower the freezing point. Then we thought that the organisms with AFP can lower the freezing point of their body fluid and is able to be less damaged.
We decided to use the AFP of the yellow mealworm Teneblio molitor. This AFP consists of 84 amino acid, right handed β-helix with 12 residues per coil. This protein has many intramolecular disulfide bonds and a rigid array of threonine side chains, which give specific TH activity about 10-100 times greater than that of fish AFP, and 300-500 times greater than those of other chemical compounds. We expressed this AFP in E.coli.
(PDB code 1ezg)
Designs of plasmids
We obtained the coding sequence of AFP which was chemically synthesized from GENEART. This gene digested with ClaⅠ was inserted into the downstream of promoter, RBS, and EGFP. In this plasmid, AFP and EGFP formed a fusion protein. In addition, we put a His tag for purification at the end of the fusion protein. This series of parts is assembled on a Low Copy vector, pSB3K3. We constructed several parts which differ in only promoter sequence. We use placIq promoter(BBa_K193207) which is constitutive promoter, T7 promoter(BBa_K193208), and inducible sequence LacO was added to T7 promoter(BBa_K193209).
Expression and Detection
We introduced the AFP plasmids into the E.coli Origami 2 strain (Novagen) and incubated 12 h at 37 ℃. Single colony was picked up from the transformed cells and inoculated into LB medium containing 30 μg/ml kanamycin. Cultures were grown at 37 ℃ with shaking (about 180rpm) to OD=0.5. The temperature was lowered to 15 ℃ and cultures were shaken for 1 h. After 1 h shaking, we added IPTG(0.5 mM final) to induce lacO. Then cultures were shaken for a 48 h at 15 ℃ after induction and harvested by centrifugation. After removing LB and adding PBS, culture boiled 5 minutes at 95 ℃ with 2×SB+2ME. SDS-PAGE electrophoresis at 120 V for 90 minutes. Then, the gel was stained by CBB (Coomassie Brilliant Blue)(Fig 1).
Results
Expression of antifreeze protein
The fusion proteins were (readily) detected by SDS–PAGE stained with CBB . The result is shown Fig 1. 1st and 2nd lanes are EGFP, 3rd and 4th lane are AFP-EGFP fusion protein. 1st and 3rd lanes with IPTG induction, and 2nd and 4th lanes were without IPTG induction. Molecular weight of EGFP-His is about 30 kDa, and AFP-EGFP fusion protein is about 40 kDa. The band of 3rd lane revealed around 40 kDa. So we regarded the protein as Antifreeze protein.
We checked expression of anti-freeze protein other way. We incubated E.coli Origami 2 which was introduce anti-freeze protein for 24 h at 37 ℃. The result of SDS-PAGE electrophoresis, the band around 40 kDa was darker than the band of incubation of at 15 ℃(not shown). However, Checking solubilization of the each proteins, there weren’t any solubilizing protein at 37 ℃, but the protein at 15 ℃ were solubilized half amount of the protein which was expressed(not shown). (This experiment done by Wakabayashi)
Discussion
Incubating E.coli introduced AFP at 37 ℃, anti-freeze protein would be expressed excessively, and E.coli would form inclusion bodies. Anti-freeze protein forming inclusion bodies wouldn’t have its activity and function to bind ice crystals.
We confirmed of the expression of the AFP in soluble fraction with 15 ℃ incubation. Therefore the expressed AFP is thought to function. Our next aim is to confirm whether the bacteria expressing AFP in solble fraction survive under low temperature like Mars environment. According to Yue and Zhang, addition of AFP into culture increased the survival rate of E.coli under low temperature. Therefore the expression of AFP might adapt bacteria to survive on the Mars environment. In our solution of terrforming of Mars, there must’ve need artificial energy to warm environment and organisms, introducing of AFP would enable it to less energy
References
- M. Bar, R. Bar-Ziv, T. Scherf, D. Fass, Efficient production of a folded and functional, highly disulfide-bonded β-helix antifreeze protein in bacteria, Protein Expression & Purification, 2006
- C. Yue, Y. Zhang, Cloning and expression of Tenebrio molitor antifreeze protein in Escherichia coli, Molecular Biology Rep (2009) 36:529-536
