Agriculture Reference
In-Depth Information
The tetraploid-cultivated peanut contains multiple copies of each
allergen gene and protein isoforms (Ramos et al. 2006). In
'
peanut (Norden et al. 1969), two isoforms of Ara h 1 and two isoforms of
Ara h 2 have been identi
'
Florunner
ed, one of each in each subgenome. Genes
encoding the two isoforms,
Ara h 2.01
and
Ara h 2.02
, are homoeologous
genes representing orthologues from diploid ancestors, most likely
Arachis duranensis (
A genome) and
Arachis ipaensis
(B genome)
(Ramos et al. 2006). In the case of Ara h 2, the open reading frames of
these two genes are highly similar, with the major difference being
insertion of 36 bp or 12 amino acids containing an extra copy of the
sequence DPYSPS, a known IgE-binding site (IgE epitope) (Stanley et al.
1997; Schein et al. 2005). While the predicted size of the proteins
encoded by
Ara h 1.01
and
Ara h 1.02
genes is 71.3 and 70.3 kDa,
respectively, the actual mature proteins extracted from seeds appear as a
single 63.5 kDa band on SDS-PAGE (Burks et al. 1991). It was found that
the N-terminal amino acid sequence of the puri
ed proteins begins at
amino acid 78 or 84, depending on the isoform (de Jong et al. 1998;
Wichers et al. 2004). These
first 78 or 84 amino acids, along with an
included 25-amino-acid signal peptide, are cleaved off during post-
translational processing. The 53- or 59-amino-acid cleaved peptides
contain six of the seven cysteines found in Ara h 1 isoforms (Wichers
et al. 2004) and three of the allergenic epitopes (Burks et al. 1997). The
number of copies of Ara h 3, a multisubunit protein, within the peanut
genome is not known, but has been estimated (Calbrix et al. 2012). Ara h
3 contains multiple isoforms (at least three of each) of acidic (40 kDa) and
basic (20 kDa) subunits. It was classi
ed as a Bowman
-
Birk trypsin
inhibitor (Dodo et al. 2004),
ed. Of these,
four (A1, A2, B1, and B3) are different only in their N-terminal regions,
which suggests they might be derived from the same gene or gene
families (Norioka and Ikenaka 1983a,b; Suzuki et al. 1987, 1993). The
amino acid sequence of the
five of which have been identi
fifth inhibitor (BII) was extremely different
and therefore reported to be encoded by a different gene. Ara h 3 is
expressed as a 60 kDa protein and then cleaved following folding into the
disul
de-linked 20 and 40 kDa subunits. Ara h 1 has been shown to have
21 IgE antibody-binding sites (or epitopes), whereas Ara h 2 has 10 and
Ara h 3 (acidic subunit) has 4 sites (Burks et al. 1997; Stanley et al. 1997;
Shin et al. 1998; Rabjohn et al. 2002). The number of epitopes on the
basic subunit differs, depending on the origin of the country from which
the peanut allergic patient serum was obtained (Burks et al. 1997;
Stanley et al. 1997; Shin et al. 1998; Rabjohn et al. 2002).
Little natural qualitative genetic variation within peanut germplasm
has been identi
ed. The most striking was an Indonesian line lacking
