Part:BBa_K4632002

Cry3A-like toxin

Description

Bacillus thuringiensis UTD-001, as well as the protoxin and toxin of this isolate, could be used to control pests such as fire ants, carpenter ants, Argentine ants, and Pharaoh's ants, including Solenopsis invicta(S. Invicta). Cry3A-like toxin isolated from UTD-001 have been shown to be toxic to S.Invicta.(Bulla and Candas, 2003)

1. How does it work?

It has been shown that after treatment with papain in vitro, the Cry3A-like toxin prototoxin (72.9 KD) forms an active toxin (66.6 KD) that is toxic to S. Invicta.(Bulla and Canda, 2003)

2. Eco-friendly and Safe

Bt (Bacillus thuringiensis) is widely recognized as a safe and environmentally benign insecticide. And the Bt toxin Cry3A-like protein we used is Eco-friendly and Safe.(see more detail on [1])

3. What we have done? (SCAU-China 2023)

In our design, the coding gene fragment for the active Cry3A-like toxin will be transformed into E. coli by the pET-30a vector, to confer the ability to produce Cry3A-like toxin. (Figure 1 )

To enable its secretion, a signal peptide sequence, OmpA, was added to the N-terminal of the Cry3A-like toxin. OmpA is a well-studied signal peptide in E.coli for the secretion of foreign proteins.

Furthermore, we fused a 6×His tag to the C-terminus of Cry3A-like toxin to facilitate subsequent protein purification and Western blot-specific characterization experiments.

Figure 1.Diagram of Cry3A-like Toxin circuit design<p>

Sequence and Features

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Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 142
  
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

Construction and Characterization

<p> 1. Verifying the Expression and Secretion Proficiency of Cry3A-like Toxin

We conducted PCR amplification on the plasmid (procured from GUANGZHOU IGE BIOTECHNOLOGY LTD) to obtain the OmpA - Cry3A-like toxin segment. Subsequently, we utilized the Gibson Assembly method with the ABclonal 2× MultiF Seamless Assembly Mix kit to clone this segment into the pET30(a) plasmid. This resulted in the creation of the plasmid pET30a-OmpA-Cry3A-like toxin, as depicted in plasmid map Figure 1. Finally, we performed a transformation of this plasmid into E. coli BL21(DE3) to assess the secretion expression of the toxin protein.

<figure align="center"> <img alt="parts1" src="" width="700" title="Construction of pET30a-OmpA-Cry3A-like toxin"

<figcaption> Figure 1: Construction of pET30a-OmpA-Cry3A-like toxin </figcaption>

</figure>

The pET-30(a)-OmpA-Cry3A-like toxin (E.coli BL21(DE3)) was cultured overnight in LB medium. The following day, the culture was subjected to transformation, and IPTG induction was carried out for 3 hours. Subsequently, the culture was centrifuged at 6,000 rpm for 10 minutes to separate the cell pellet and the supernatant. Afterward, both fractions were subjected to SDS-PAGE analysis (as shown in Figure 2)

<figure align="center"> <img alt="parts1" src="" width="700" title="SDS-PAGE analysis of Cry3A-like toxin expression"

<figcaption> Figure 2: SDS-PAGE analysis of Cry3A-like toxin expression lane1:Concentrated protein supernatant of pET-30a(+IPTG); lane2:Concentrated protein supernatant of pET-30a-OmpA-Cry3A-like toxin(+IPTG); lane3:Concentrated protein supernatant of pET-30a-OmpA-Cry3A-like toxin(-IPTG) </figcaption>

</figure>

The supernatant from the induced culture displayed a distinct 66.6 kDa band corresponding to Cry3A-like toxin, which was absent in the supernatant of the non-induced culture and the wild-type control. This observation confirms the successful secretion expression of Cry3A-like toxin.

Subsequently, we utilized the enzyme digestion ligation/ΩPCR method to add a 6×His tag to pET30a-OmpA-Cry3A-like toxin. This modification was carried out to facilitate Western blot experiments, further confirming the secretion expression of Cry3A-like toxin (as depicted in plasmid map Figure 3).

<figure align="center"> <img alt="parts1" src="" width="700" title="Construction of pET30a-OmpA-Cry3A-like toxin with a 6×His tag"

<figcaption> Figure 3: pET30a-OmpA-Cry3A-like toxin with a 6×His tag </figcaption>

</figure>

2. Poisonous protein validation model

(1). Determination of ligand protein

We retrieved the amino acid sequence of the cadherin-like protein BT-R1 [ 2 ] from Manduca sexta in the NCBI database, which has been identified to interact with Bt Cry protein, and paired it with its homologous protein cadherin-23 in S.invicta using blast.

(2). Protein modeling and protein-protein docking

The homologous modeling of Cry3A-like protein and cadherin-23 was performed using swiss-model. The modeling results are as follows ( cadherin-23 left, Cry3A like protein right,

see Cry3A _ like _ protein.pdb, Cry3A _ like _ protein.stl, cadherin-23.pdb, cadherin-23.stl <a href="https://2023.igem.wiki/scau-china/model" class="pr-0" target="_blank">(scau-china/model)</a>).
<figure align="center"> <img alt="parts1" src="" width="600" </figure>

We used GRAMM ( Global RAnge Molecular Matching ) to dock our toxic proteins and ligand proteins. PDBePISA was used to analyze the docking results. The docking mutual surface size was 2465.8, and the binding free energy was-4.2. The binding free energy was less than 0, and the docking was meaningful.
<figure align="center"> <img alt="parts1" src="" width="700" </figure>

Among them, the hydrogen bonds and salt bridge sites formed by protein docking are shown in the following table.
<figure align="center"> <img alt="parts1" src="" width="700" </figure>

The docking surface is shown in the following figure ( see the docking.pdb, docking.x3d file [2]).
<figure align="center"> <img alt="parts1" src="" width="700" </figure>

<p>(3). Molecular dynamics simulation of protein-protein complex

The dynamic simulation of the protein is shown in the section Existing problems and future work in https://2023.igem.wiki/scau-china/model

References

Lee A. Bulla, Jr.Mehmet Candas Formicidae (ant) control using Bacillus thuringiensis toxin US 6,551,800B1[P]. 2003-04-22.

Han, L., Zhao, K., & Zhang, J. (2009). Interaction between insect calreticulin and Bt Cry1A protein. Insect Knowledge, 2009(2), 7. DOI: CNKI:SUN:KCZS.0.2009-02-007.