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.