Structural studies on native and chemically modified storage proteins from rapeseed (Brassica napus L.) and related plant proteins

Abstract

Recent data on the structure and chemical modification of the two main storage proteins of rapeseed, the high-molecular mass 12 S globulin and the low-molecular mass 2 S protein (napin) are summarized and compared with those of related seed proteins. The 12 S globulin is built up of six subunits forming a quaternary structure which can be approximated by the model of a trigonal antiprism. The subunits, composed of a larger and a smaller polypeptide chain each, have a two-domain structure which is typical for all related plant proteins. These are characterized by a sedimentation coefficient of 11-13 S, a molecular mass of 300,000-360,000 g/mol and a high percentage of beta-sheet conformation. Increasing succinylation results in a step-by-step dissociation up to the subunits and to an unfolding of the latter at a critical level of modification amounting to 60-70%. These structural changes affect the functional properties remarkably. The napin fraction comprises a group of closely related and highly basic proteins with molecular masses of 12,000-14,000 g/mol, a high content of sulphur-containing amino acids and rich in helical conformation. They are built up of a larger and a smaller disulphide bridged polypeptide chain. Acylation does not abolish the secondary or tertiary structure which are stabilized by inter- and intrachain disulphide bonds. Acylation results, however, in a stabilization of the protein against heat-induced aggregation.

Selected functional properties of detoxified rapeseed protein preparations effected by phytic acid

“…The shifting of the isoelectric range of the protein isolates dependent on the PA content is in agreement with the results presented by Schwenke et al [16,17]. Based on the method of turbidimetric titration they have investigated the interactions (complexation) between phytic acid and repeseed globulin (12 S globulin with a molar mass of 300 OOO g mol", and an isoelectric point of 7.2) and rapeseed albumins with molar masses of 13 OOO -15 OOO mol-I, with isoelectric points >10 and with a high content of basic protein groups, respectively.…”

Rapeseed use in aquaculture

“…Napin is composed of two polypeptide chains with molecular weights of 9 and 4 kDa, linked by disulfide D105, page 5 of 9 bonds. Cruciferin is consisted of 6 subunits and each subunit contains smaller units (polypeptide chains) with molecular weights in the range of 18.5 to 31.2 kDa, linked by disulfide bonds (Schwenke et al, 1973;Schwenke et al, 1983;Mieth et al, 1983;Schwenke, 1990). Based on the SDS-PAGE assay the both storage proteins were observed in the produced protein product concerning the detected bands with molecular weights of 31-29, 24-21 kDa for cruciferin polypeptide chains and 9-4 kDa for napin polypeptide chains.…”

“…Due to the different amino acid sequence of the both proteins the produced RPC may have a slightly different amino acid composition from the starting meal. For example, napin is rich in lysine (the most limiting amino acid in all oilseed proteins) as well as sulfur containing essential amino acids like methionine and cysteine (Ericson et al, 1986;Schwenke, 1990;Wanasundara et al, 2010). Exactly the content of these amino acids has increased in the RPC dramatically.…”

Rapeseed Proteins for Paperboard Coating

“…The acetylation was performed according to the procedure of Schwenke [10]. A 5 % mixed protein solution was dissolved in phosphate buffer and reacted with acetic anhydride (0.25 g anhydride g protein ) at pH 7.7 for 1 h at room temperature (23 ± 2°C).…”