Polypeptides associated with camelina meal
The polypeptides associated with mucilage-reduced, oil-free camelina
meal were examined by SDS-PAGE (Figure 3A). The 44.1 kDa and 51.7 kDa
polypeptides detected under non-reducing conditions are likely monomers
of cruciferin similar to those reported for B. napus canola
(Nietzel et al., 2013; Perera et al., 2016; Wanasundara, 2011). S-S
bonds stabilize these polypeptides since bands between 20 and 39 kDa
observed under reducing conditions may be similar to the α- and β-chains
of cruciferin. The 14 kDa and 10.4 kDa polypeptides observed under
non-reducing and reducing conditions, respectively, are characteristic
of napins, which also contain a S-S bond (Wanasundara, 2011).
Polypeptide profiles of defatted camelina meal reported by Boyle et al.
(2018) and Naugen et al. (2013) also indicated bands representing
cruciferin and napin. Apart from these, 15-20 kDa polypeptides also were
present. Boyle et al. (2018) speculated that the ~15 to
20 kDa polypeptides found in highly alkaline extracts (pH 12) of
camelina meal might be glutelins; however, they are most likely oleosins
associated with OBPs as reported for canola (Wijesundera et al., 2013).
The lightly stained polypeptides between 67 kDa and 69 kDa may be
membrane-bound proteins, aggregates of cruciferin free chains or
unidentified SSPs.
Polypeptide profiles obtained for the enriched cruciferin (Figure 3B; pH
8.5 extraction) and napin (Figure 3C; pH 3 extraction) fractions showed
that the majority of intensely-stained bands were related to cruciferin
and napin, respectively, similar to those of other crucifers, such asB. napus (Perera et al., 2016), Sinapis alba (Marambe et
al., 2015; Wanasundara et al., 2011) and A. thaliana(Withana-Gamage et al., 2013) obtained using a similar separation
process. Electrophoretic separation of the fractions under native
conditions showed that cruciferin was present in both trimeric and
hexameric forms (Figure 3D), while napin was monomeric (Figure 3E),
keeping in mind that both cruciferin and napin monomers consist of two
polypeptides linked via S-S bonds.