Difference between revisions of "Part:BBa K4197009"

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Gene coding for Gal d 2

Gene coding for the egg allergen called Gal d 2.

Introduction

This part is composed of the gene coding for the allergen of Hen’s egg Gal d 2 (NCBI: V00383.1). The Hen's egg allergy prevalence is 0,5-2,5% in developped countries and Gal d 2 compose 54% of its dry mass (Palosuo and al. 2018). Gal d 2 have already been expressed in Express Iq E. coli and was able to bind the IgE of patient with egg's allergie (Dhanapala and al. 2015). Gal d 2 was merged to the membrane protein OmpA of E. coli from part BBa_K1694002. This lippoprotein is the most abundant in E. coli's membrane with 100,000 copies per cell (Ortiz-Suarez and al. 2016) and is often used to display protein on the surface of bacteria (yang and al. 2016).

Construction

OmpA_Gal d 2 fragment from IDT gblock was amplified by PCR using the high fidelity Phusion polymerase with primers FORWARD: gccgcaagctttaatgatggtgatggtgatggtgatg) and REVERSE: cgagctccgtcgacaaggaggtaatatacatatgaaagcc. Expected size of the amplicon was 1675 bp.

pET-21 b (+) vector was linearized by PCR using the high fidelity Phusion polymerase with primers FORWARD:tgtcgacggagctcgaattcg and REVERSE:ttaaagcttgcggccgcactcg. Expected size of the amplicon was 5442 bp.

Amplification product sizes were checked on EtBr stained agarose gel (Figure 1).

Figure 1: pET-21 b (+) linearized (A) and Gal d 2 amplified fragment (B). Expected sizes of the amplicons were 5442 bp (A) and 1675 bp (B). PCR amplicon sizes of pET-21 b (+) (A) and Gal d 2 (B) were checked with agarose electrophoresis gel and revealed with EtBr. A theoretical gel is presented with each gel and the NEB 1 kb DNA ladder is used for the experimental gels. (note that a different ladder is presented on the theoretical gel).

Amplification products matched the expected size, they were further purified from gel.

The Gal d 2-OmpA construction was then inserted into pET-21 b (+) by In-Fusion. The resulting products were transformed into Stellar competent cells. Transformants were selected on LB-ampicillin plates. 20 transformants were screened by colony PCR with primer pairs flanking the insertion zone (FORWARD: ggttatgctagttattgctcagc and REVERSE: ccgaaacaagcgctcatgagc, expected size of the amplicon : 2092 bp). 2 positive transformants were detected (Figure 3).

Figure 2: identifying fragments that bear pET21 b (+)_Ompa_Gal d 2 by colony PCR. Expected size of the amplicon was 2092 bp. The positive clones were colonies 17 and 24. PCR amplicon sizes of colonies with Gal d 2 plasmid were checked with agarose electrophoresis gel and revealed with EtBr. A theoretical gel is presented with each gel and the NEB 1 kb DNA ladder is used for the experimental gels (note that a different ladder is presented on the theoretical gel).

These transformants had their plasmid extracted by Miniprep and digested by EcoRV to assess the assembly (expected fragments at 4332 bp and 2785 bp, see Figure 4).

Figure 3: restriction profile of pET-21 b (+)_OmpA_Gal d 2 final construction. Enzyme used was EcoRV. Expected sizes of the amplicons were 4332 bp and 2785 bp. Plasmids were checked with agarose electrophoresis gel and revealed with EtBr. A theoretical gel is presented with each gel and the NEB 1 kb DNA ladder is used for the experimental gels (note that a different ladder is presented on the theoretical gel).

The correct restriction maps were obtained and the insert sequence was further validated by sequencing. The plasmid was named pET-21 b (+)_OmpA_Gal d 2. The plasmids were eventually used to transform E. coli Tuner cells in order to express the OmpA_Gal d 2 construction at the cell membrane. But no proof was obtain of the expression.

References

1. Dhanapala, P., Doran, T., Tang, M. L. K., & Suphioglu, C. (2015). Production and immunological analysis of IgE reactive recombinant egg white allergens expressed in Escherichia coli. Molecular Immunology, 65(1), 104–112. https://doi.org/10.1016/j.molimm.2015.01.006
2. Palosuo, K., Kukkonen, A. K., Pelkonen, A. S., & Mäkelä, M. J. (2018). Gal d 1-specific IgE predicts allergy to heated egg in Finnish children. Pediatric Allergy and Immunology, 29(6), 637–643. https://doi.org/10.1111/pai.12954

Sequence and Features