3. Results
3.1. PCR amplification of the egg white allergen cDNA
The mRNA isolated from chicken oviduct were used to PCR
amplify egg white allergens Gal d 1, 2 and 4 using one-step PCR
method. For Gal d 3, a long-range PCR, that utilises the traditional
two-step method, was used. The PCR gel results showed a band for
Gal d 1 at 800 bp (expected 630 bp), Gal d 2 between 800–2000 bp
(expected 1158 bp), Gal d 3 at 2000 bp (expected 2115) and Gal d
4 at above 400 bp (expected 441) (Fig. 1). The long-range PCR conducted
for Gal d 3 produced a brighter band when used without
Q-solution (Fig. 1).
3.2. Cloning and expression of recombinant egg white allergens
The amplified PCR products were then digested by restriction
enzymes and ligated into pTrcHisA vector that adds a 6xHis
tag to the expressed proteins. The vector-insert constructs were
transformed into Express I
q chemically competent E. coli cells and
expression induced with IPTG. Expression was conducted for 6 h
and samples were collected every 1-h to determine the optimum
expression time for each allergen. The collected samples were pelleted,
lysed and the soluble and insoluble fractions were run on
SDS gels for analysis. These gels were then western blotted, incubated
with detection antibody and visualised with a chromogenic
substrate. For Gal d 1 and 2, the western blot analysis showed
that the proteins are found in both soluble and insoluble fractions
with an optimum expression time of 2 h. Gal d 2 shows increase
in expression every hour, at the same time showing an increase
of breakdown of the protein. Gal d 3 and 4 showed expression
only in the insoluble fraction, with an optimum expression time
of 2 h. Gal d 3 showed breaking down of the protein throughout the
expression period, while Gal d 4 showed a decrease in the amount
of protein after 2 h and increasing again in 5–6 h (Fig. 2).