Biochemical characterisation of a novel polymeric protein subunit from bread wheat (Triticum aestivum L.)

A new wheat endosperm protein subunit that was found in accessions belonging to different collections was identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Insoluble in 0.5 M NaCl, 70% ethanol, dimethyl sulphoxide (DMSO) and 50% propan-1-ol, it appeared in the pellet corresponding to the polymeric proteins along with high (HMW) and low molecular weight (LMW) glutenin Subunits (GS). In the reduced form, it had an electrophoretic mobility between those two types of glutenin subunits. The apparent M-s, of this novel protein was estimated by SDS-PAGE to be 71 000. N-terminal sequence and amino acid analyses indicated a composition similar to the omega-gliadins encoded by genes located on chromosome 1B. This protein can be ascribed to the D-subunits of LMW-GS with at least one cysteine residue that allows it to form part of the polymeric structure of glutenin, as shown by reaction with a fluorogenic reagent specific for sulphydryl groups. Fractions collected after size exclusion high-performance liquid chromatography (SE-HPLC) fractionation and further characterised by SDS-PAGE, confirm that the protein participates in the glutenin polymeric structure. An increase in its concentration was observed in fractions collected within the polymeric peak as elution time increased, implying that a larger amount of this protein is present in small size polymers. The role of this protein in the complex relationship between endosperm proteins and quality parameters is discussed in relation to its likely role as a chain terminator. (C) 2002 Elsevier Science Ltd.