A comparative study of the structural and physicochemical properties of the major proteins from Camelina sativa (L.) Crantz and Brassica napus L.

Abstract

Camelina sativa (L.) Crantz is a new industrial oilseed crop suitable for the Canadian prairies and which shows potential benefits for the Canadian bio-economy. This study was carried out to identify the major proteins of the oil-free residue (meal) of C. sativa (camelina) while investigating their structural and physicochemical properties. Canola (Brassica napus L.) was used as the control in the study. Camelina seeds were treated with Viscozyme® (0.1 mL/g) to remove mucilage. The mucilage free meal contained 51.3% protein (dwb, %N×6.25) which was greater than in canola. Both camelina and canola meals shared similar profiles for polypeptides and amino acids. At acidic pHs, canola meal had higher soluble protein content than did camelina meal, but the opposite was observed when the pH moved toward alkaline. A pH of 4.5 identified as the apparent isoelectric point (pI) of the protein from these two meals, which is presumably a cruciferin-napin complex. The 11S and 2S proteins of both seed types were isolated and purified using liquid chromatography. The purified 11S protein from camelina and canola contained predominantly cruciferin with minor contamination with non-targeted storage proteins. Of the non-cruciferin contamination of camelina, vicilin (7S) found to be abundant. The purified 2S protein from camelina contained napin and a noticeable amount of late embryogenesis abundant (LEA) protein, whereas non-napin contamination was minor in canola. In camelina, cruciferin, napin and vicilin expressed from eleven, four and six genes, respectively, were identified. The oil body proteins were also isolated and several isoforms of oleosin were found in camelina and canola, whereas putative isoforms of caleosin and steroleosin were found only in camelina. The structural and physicochemical properties of cruciferin and napin were studied in response to changing pH and temperature. The predominance of beta-structure and α-helix content in the 2˚ structure of cruciferin and napin, respectively, was confirmed for both camelina and canola. Cruciferin from camelina and canola exhibited acid-induced structural unfolding at the 3˚structure level. Cruciferin was not completely unfolded and assumed an intermediate state, plausibly a molten globule. Napin structure was not as sensitive as cruciferin to changing medium pH or an increase in temperature. Cruciferin exhibited high thermal stability (>80˚C) at neutral and alkaline pH, whereas the opposite was observed at acidic pH. Results showed that the cruciferin and napin responded differently to changing pH and temperature. Therefore, conditions of oil extraction and protein recovery from meal may affect these two storage proteins differently.