Team:HokkaidoU Japan/co-expression
Co-expression System
Overview
If we need antimicrobial peptides (AMPs), we usually get it from chemical synthesis method because its amino acid residues are less than another peptide. However chemical synthesis method is unsuitable for the case which a large amount of isotopically labeled peptides is essential for structural study by NMR. In this case, we’ll choose the recombinant synthesis method but, of course, AMPs are harmful to host bacteria. To prevent host toxicity, there is the solution which utilizes expression with inclusion bodies. In addition, in case that it is not promising to form inclusion bodies, we make a partner protein which has the high potential to form inclusion bodies co-express with protein of interest.
- ABF-2
- Lactalbumin family
- Application of co-expression system to Thanatin
ABF-2 is one of the AMPs derived from Caenorhabditis elegans. ABF-2 belongs to the CSαβ superfamily which has both α-helix and antiparallel β-sheet stabilized by some disulfide bonds and interacts to cell membrane like thanatin. It is difficult for ABF-2 to form inclusion bodies alone. So the recombinant synthesis method by co-expression system may be effectible.
We choose four Lactalbumin family proteins, concretely HLA (Human α-Lactalbumin), BLA (Bovine α-Lactalbumin), HLZ (Human Lysozyme), BLZ (Bovine Lysozyme), as partner proteins. Because these proteins have negative charge and ABF-2 have positive charge like thanatin, they will interact and form inclusion bodies. There is study which used these proteins for formation of inclusion bodies with ABF-2. (2013. S. Tomisawa et al.)
Because, as referred to above, thanatin also has positive charge, it is projected that thanatin interacts Lactalbumin family proteins which have negative charge. For reference, the isoelectric point (pI) of ABF-2 is 9.1, on the other hand, pI of thanatin is 10.47. On the other hand, pI of HLA is 4.7, BLA is 4.8, HLZ is 9.3 and BLZ is 6.5. We think the value of pI of thanatin is enough similar with ABF-2 to apply this method for ABF-2 to thanatin.
Design
- Constructs
First of all, we made the construct like Figure 1 (Pbad-B003x-HLA family-dT on 1C3).
Figure 1. The construct of partner proteins
On the other hand, we also made the construct like Figure 2 (Plac-B0034-AMPs-dT on 1C3).
Figure 2. The construct of AMPs
Then, we picked up the Plac-B0034-AMPs-dT as fragment from the latter construct and introduce it upstream like Figure 3.
Figure 3. The complete construct of Co-expression system
Finally, we can induce only thanatin or ABF-2 (AMPs) by IPTG (glucose) and only partner proteins (HLA family).
Experiments
We research which partner proteins is the most suitable for formation of inclusion body with thanatin by using the constructs described above. (HLA, BLA, HLZ or BLZ) And we also research the effect of intensity of RBS by changing it. (B_0032, B_33 or B_0034) In addition, we can get the activation form of thanatin by heating or ionic strengths.
- How assay
- Activity test for ABF-2 and Thanatin →Comparing growth curve between the samples one is induced by IPTG and the other is not induced.
- Diluting the bacterial culture which is enough pre-cultured by 0.1 O.D.600 (Optical Density in λ=600nm) in 2ml LBC.(Lysogeny Broth liquid culture including chloramphenicol)
- Adding 2µl of IPTG into one and DW into the other.
- Measuring O.D.600 of these samples once in an hour.
- Repressing test of AMPs’ activity by co-expression system →Comparing growth curve among the different induction patterns, induced by IPTG, arabinose or not.
- Diluting the bacterial culture which is enough pre-cultured by 0.1 O.D.600 (Optical Density in λ=600nm) in 2ml LBC.(Lysogeny Broth liquid culture including chloramphenicol)
- Adding 2µl of IPTG and 200µl of arabinose into sample 1, 2µl of DW and 200µl of arabinose into sample 2, 2µl of IPTG and 200µl of DW into sample 3 and 202µl of DW into sample 4.
- Measuring O.D.600 of these samples once in an hour.
First of all, we make sure that the constructs have correct sequence by sequencing.
If we get the expected constructs, we transform it into E.coli (in this case, we used DH5alpha) and compare the growth curve among different inductive condition.
*In this experiment, we should also make sure that the AMPs induced by IPTG are surely effective to growth curve by changing inductive timing or amount of IPTG.
*In this experiment, we should change different patterns of constructs, for example changing strength of RBS or kind of partner proteins.
Result
We could make only two constructs, BBa_K1714004 (Pbad-B0034-BLA family-dT on 1C3) (Fig.4) and BBa_K1714001 (Plac-B0034-ABF-2-dT on 1C3) (Fig.5). We made sure that these constructs have correct sequence but BBa_K1714001 is not sequenced correctly in some part of it.
Figure 4. The simple construct of BBa_K1714004
Figure 5. The simple construct of BBa_K1714001
We also made E.coli (DH5alpha) which includes BBa_K1714001 plasmid for activity test of ABF-2 and carried out the activity test. (How Assay 1) There is a result of the test as Table 1.
Chart 1. The growth curve of E.coli including BBa_K1714001 with IPTG or not
As you can see, we can’t say that ABF-2 in BBa_K1714001 has antimicrobial activity.
Conclusion
However we could make sure that BBa_K1714001 has almost correct sequence, we couldn’t make sure that ABF-2 in BBa_K1714001 has antimicrobial activity. It means that the ABF-2 doesn’t express appropriately by any cause. As one of the supposable reason, because ABF-2 is toxic to E.coli, the mutated one which is not toxic to E.coli is selected in transfer E.coli into new culture again and again. We can also imagine that this is something to do with that the sequence of BBa_K1714001 wasn’t perfectly correct or we could get the colonies of E.coli including AMPs by DH5alpha which is less repressive efficiency of lac promotor than JM109. (We couldn’t get constructs including thanatin by DH5alpha)
We couldn’t registry the expected construct which is Plac-B0034-ABF-2-dT -Pbad-B0034-BLA family-dT on 1C3 (like Figure 3) but we can co-express these two constructs in another way. It’s transferring one or the other construct to another plasmid which has another origin and transforming them together. However there is a potential of fail to repress the toxicity by co-expression system because of the difference of copy number of plasmids. For this problem, we should find solution experimentally through trial and error for example changing the strength of RBS, the amount of Inductive materials or the timing of induction.
In this year, because of the lack of time, we couldn’t accomplish the expected experiments in this project. However if we accomplished all experiments we expected and found the best pattern to make inclusion body for thanatin, we may consider so many things. According to the paper (2013 S. Tomisawa et al.), BLA is the best partner protein to make inclusion body for ABF-2. If the value of isotonic point (pI) is main factor to form inclusion body, we can expect that BLA is also the best one for thanatin because the value of pI of thanatin is similar with ABF-2. On the other hand, if we find another protein the best one to form inclusion body for thanatin, the relation with interest protein and partner protein is not only due to the value of pI but other factors for example structure and so on. Originally, because there are so many proteins which have positive charge, it is difficult to form inclusion body only by pI factor. So, if we made all expected constructs, we can’t surely repress the toxicity of thanatin by co-expression system of these four kinds of Lactalbumin family proteins.
Anyway, we should experiment for longer time and get any result about co-expression system. By doing this, not only we can standardize the expression of proteins which have host toxicity and make smooth it, but also we may found something new about AMPs which have many question marks in structural part.
Reference
Tomisawa, S., Hojo, E., Umetsu, Y., Ohki, S., Kato, Y., Miyazawa, M., ... & Aizawa, T. (2013). Overexpression of an antimicrobial peptide derived from C. elegans using an aggregation-prone protein coexpression system. AMB Express, 3(1), 45.
