A proteomic approach to the identification and characterisation of protein composition in wheat germ

Abstract

Proteome analyses were carried out on commercial wheat germ of mature grain from the biscuit-making wheat cultivar, Rosella. Wheat germ protein extracts were fractionated by two-dimensional gel electrophoresis across two different immobilised pH gradients: pH 4.0-7.0 and 6.0-9.0. A total of 612 individual protein spots were excised from the gels and characterised by peptide mass fingerprinting. From these analyses, 347 individual proteins were identified from protein sequence database interrogation, and 301 different types of protein were catalogued according to protein function. The remaining 265 protein spots gave poor or no matches to proteins in the databases and were not identified in this study. Six different classes of enzymes were identified in the germ, many of them having roles in the mobilisation of energy reserves for germination. Abundantly expressed enzyme classes include the oxidoreductases, transferases and hydrolases. A comparison was also made between the major protein classes expressed in the germ and protein classes expressed in the endosperm from previous proteomic work. This study contributes significantly to our knowledge of protein expression and heterogeneity in the germ of wheat grain and forms the basis for future studies in regard to the characterisation of proteins during the initial stages of germination.

Strategic Distribution of Protective Proteins within Bran Layers of Wheat Protects the Nutrient-Rich Endosperm

“…However, the major protein class in terms of spot number (387 spots or 58%) was identified as the 7S globulin storage protein (globulin 3 protein) of the cupin superfamily. Although previously reported in wheat grain (Robert et al, 1985), this protein was not identified as a component in the endosperm (Skylas et al, 2000) or germ (Mak et al, 2006) and has not been localized in wheat grain. It has been speculated that in addition to their storage protein function, 7S globulins may offer some protection against oxalic acid (Dunwell et al, 2000) produced by pathogenic fungi (Donaldson et al, 2001;Lane, 2002).…”

“…Their location within the grain has not been identified explicitly and is usually assumed to be in the endosperm (Gebruers et al, 2001). Other reported proteomic analyses of wheat grain did not identify these proteins in the endosperm (Skylas et al, 2000) or embryo (germ; Mak et al, 2006), suggesting that they are likely to be exclusively located in the bran. Our proteomic and confocal immunomicroscopy results show that XIP-I is highly concentrated within the nucellar layer (Figs.…”

“…Proteomic analysis of wheat grain has previously been applied to identify proteins in the germ and endosperm (Skylas et al, 2000;Wong et al, 2004;Mak et al, 2006), but analysis of bran and bran tissue fractions has not been reported. Collection of sufficiently pure bran tissue fractions has limited progress, mainly due to the strong bonds between the various bran tissue layers and endosperm in dry grain.…”

Using proteomics to study sexual reproduction in angiosperms

“…The results from separate proteomic analyses of developing wheat ) and rice (Xu et al 2008) endosperm, and wheat (Mak et al 2006) and rice embryos (Woo et al 2002;Wang et al 2008) highlight the differences in these two seed organs (Table 1). The CM proteins were the most abundant in all instances; however, members of the PF category were relatively more abundant in endosperm, while proteins included in the SR and HS categories were more abundant in embryos.…”

“…Using a 2-DE plus either MALDI-TOF PMF (Finnie et al 2002;Vensel et al 2005;Finnie and Svensson 2009) or LC-MS/MS (Méchin et al 2004;Mak et al 2006;Xu et al 2008;Kim et al 2009) experimental design, a total of 1,496 proteins were identified. When the proteins are separated into the same 10 functional classes that have been used throughout, the distribution is as follows: CM, 34%; CS, 12; SR, 5; NA, 2; PS, 2; PF, 5; PT, 7; HS, 2; MT, 2; and PUF, 29.…”