2.4. Mass spectrometry analysis of the recombinant proteins
Selected gel bands of the optimum time points of each allergen
(2 h) were incised and subjected to mass spectrometry analysis.
The gel bands were in-gel-digested with trypsin and incubated
overnight at 37 ◦C to digestthe proteins into peptides. In-gel-digest
samples were analysed on a LTQ Orbitrap Elite (Thermo Scientific)
coupled to an Ultimate 3000 RSLC nanosystem (Dionex). The
nanoLC system was equipped with an Acclaim Pepmap nano-trap
column and an Acclaim Pepmap analytical column. 2 l of the
peptide mix (i.e. each digested band) was loaded onto the trap
column of 3% CH3CN containing 0.1% formic acid for 5 min before
the enrichment column is switched in-line with the analytical column.
The LTQ Orbitrap Elite mass spectrometer was operated in
the data-dependent mode, whereby spectra were acquired first
in positive mode followed by collision induced activation (CID).
Ten of the most intense peptide ions with charge states ≥2 were
isolated and fragmented using normalized collision energy of 35
and activation Q of 0.25 (CID). Data analysis was carried out
using Proteome Discoverer (Thermo Scientific version 1.4) with
Mascot against the BIRDS database. Search parameters were precursor
mass tolerance of 10 ppm, fragment mass tolerance of 0.6 Da
(CID). Carbamidomethyl of cysteine was set as fixed modification
and oxidised methionine as a variable modification. Trypsin
with maximum of 1 missed cleavage was used as the cleavage
enzyme.