Vicilins
Eight vicilin isoforms are encoded by genes in the camelina genome
(Supplementary Table S1), of which six were identified in 13 2DE spots
from the cruciferin-enriched fraction (Supplementary Table S2). These
six isoforms accounted for 0.2-10.2% of the total protein in the 13
spots. CsVic1B-1-G2 and CsVic2-1-G2 were not found in the
cruciferin-enriched, napin-enriched or oil body protein fractions
(Supplementary Tables S2-S5). The most prevalent vicilin isoform was
CsVic1A-1-G1 (Csa19g031870, 11 spots), followed by CsVic1A-1-G2
(Csa01g025880, 7 spots), CsVic1B-1-G3 (Csa15g039300, 7 spots) and
Csa05g038120 (6 spots). Vicilin is a 7S trimeric globulin found mainly
in legumes (Shewry et al., 1995). Similar to cruciferin, vicilin is a
cupin super-family protein containing a characteristic ‘jelly-roll’
β-barrel domain (Shewry et al., 1995); however, it forms a trimeric
quaternary structure as the protomer is not processed and lacks the
internal S-S bond present in cruciferin that is involved in structural
changes associated with hexamer assembly. Mature trimeric vicilins have
molecular weights of ~ 150-200 kDa (Shewry, 1998).
Camelina vicilin protomers ranged from 462-535 amino acids
(Supplementary Figure S2) with molecular weights between 52.0 kDa and
58.5 kDa and migrate with cruciferin subunits in SDS-PAGE gels under
non-reducing conditions, but are separable under reducing conditions.
The ~69 kDa and ~53 kDa polypeptides
observed in camelina meal under reducing conditions (Figure 3A) may be
vicilins. Some vicilins, such as that from pea (Casey et al., 1986), are
proteolytically-processed yielding smaller polypeptides. If this is also
the case for camelina vicilins, they might migrate with the free α- and
β-chains of cruciferin (Figure 3B). Delseny and Raynal (1999) and Shewry
and Casey (1999) reported two genes, AtPAP85 (Q9LUJ7) and AtVCL22
(Q9SK09), that encode 7S proteins in A. thaliana that were highly
similar to pea vicilin and related legume 7S proteins.