Latest revision as of 04:50, 2 October 2024

Cry6Aa2 is a Nematocidal crystal protein from Bacillus thuringiensis YBT-1518

Cry6Aa2 is a crystalloprotein that kills nematodes.It is able to enter the gut of the nematode worm and trigger a necrosis pathway different from other Cry proteins.Total structure weight of Cry6Aa2 protein is 48.23 kDa^[1].Cry6Aa2 can be expressed in Escherichia coli BL21 (DE3) and exert its toxicity.

Sequence and Features

Usage and Biology

As a Gram-positive bacterium, Bacillus thuringiensis produces a variety of insecticidal crystal proteins during its growth. In the past hundred years, Bacillus thuringiensis has been widely developed and studied as a microbial insecticidal agent. The gene encoding the insecticidal crystal protein is the main source of transgenic insect-resistant plants. Cry6Aa2 is a crystal protein from Bt YBT-1518 that kills nematodes through a specific necrotic pathway^[2]. In our project, we fused Cry6Aa2 with SpyCatcher, attached it to virus-like particles with SpyTag, and released it into the soil environment to kill nematodes through the cleavage of engineered bacteria.

Figure 1. Cry6Aa2-6*His(pET28a)plasmid vector

Characterization

Colony PCR

We designed an forward primer inside the cry6Aa2 gene sequence and a reverse primer on a linearized vector to serve as a primer for our colony PCR, as this may reduce the production of false positives.We chose 2× Magic Green Taq SuperMix.It contains DNA Polymerase, dNTP, and an loading buffer system.The PCR reaction consisted of 15 μL 2 × Magic Green Taq SuperMix, 1.5 μL forward primer (3.75 mM), 1.5 μL reverse primer (3.75 mM), 11 μL ddH₂O and 1 μL colony.

Agarose gel electrophoresis

The success of vector construction was verified by colony PCR of Escherichia coli BL21(DE3)

Figure 2. M: DL2000 DNA Marker; 1-6: Colony PCR bands for Escherichia coli

Cry6Aa2 expression condition

The bacteria were inoculated in 15 mL LB medium of 50 μg/ml kanamycin sulfate and cultured at 37℃ for 8 h. When OD₆₀₀ reached 1.0, the induction group was induced with 1M IPTG at 16℃ overnight. The non-induced group was cultured overnight at 16℃ without IPTG.

Purification of Cry6Aa2

The cultured 15 mL bacterial solution was centrifuged at 8000 rpm at 4℃ for 10 min to discard the supernatant. An appropriate amount of PBS was added to re-suspend the washing bacteria, and then the previous centrifugal operation was repeated. The bacterial suspension was obtained by re-suspension with 3 mL Binding Buffer.
The cell lysate was obtained by ultrasonic crushing of lytic bacteria, centrifuged at 12000 rpm at 4℃ for 15 min, and the supernatant was transferred to a new EP tube.
Cry6Aa2 protein was purified by Ni-NTA column using gravity method. The supernatant and Binding Buffer were mixed in equal amounts to make the sample, and the sealing solution was slowly discharged. 5 mL Washing Buffer was used to balance the Ni column, and the sample was placed on the column at twice the column volume each time, and the first washing solution was placed on the column again.Wash the column with twice the column volume of Washing Buffer and collect the runthrough until the runthrough absorbance approaches the baseline at 280 nm. Eluting with twice the column volume of the Elution Buffer, 2 mL eluent is collected at a time until the absorbance of the eluent approaches the baseline at 280 nm. The purified sample was obtained.

SDS-PAGE

Figure 3. A:SDS-PAGE for Bacterial protein;B: SDS-PAGE for purification of bacterial protein
M:Protein marker;Ctrl:Escherichia coli BL21(DE3)without an imported vector.1, 2, 3 and 4 were Escherichia coli BL21(DE3) introduced into Cry6Aa2-6*His(pET28a).1 and 3 were induced without IPTG, and 2 and 4 were induced by 1 M IPTG.