A MALDI-TOF based study of the in-vivo assembly of glutenin polymers of durum wheat

•MALDI-TOF investigation was conducted on wheat storage protein from immature grains.•Newly synthesized glutenin subunits carried several reduced cysteine.•Cysteine assumed as part of disulfide bonds might be partly S-glutathionylated.•Oxidative folding of low-molecular weight subunits is a late event.

Wheat grain is recognized as the most suitable raw material for bread and pasta making due to the unique viscoelasticity of its storage proteins, and in particular its glutenin polymers. During grain development, low molecular weight (LMW) and high molecular weight (HMW) glutenin subunits (GS) gradually assembled through inter-chain disulfide bonds. Despite the impact of the final glutenin polymer size distribution on wheat technological quality, little is known concerning the oxidative folding of GS. In particular, which of their cysteine (Cys) residues participate to GS inter-chains remains putative. In this study GS from immature Triticum durum wheat grain were separated (1D SDS-PAGE) and digested into peptides, which were analyzed by MALDI-TOF/TOF. Differential alkylation of free and disulfide bonded Cys allowed us to identify the oxidative folding state of five types of LMW-GS and of the 1Bx20 HMW-GS. GS as monomers or as part of small oligomers carried a high number of free cysteine residues. In addition, some Cys residues, hitherto assumed as involved in intra-chain disulfide bonds, appeared simultaneously in free and oxidized forms. The last result could be assigned to their partial-blocking by glutathione. We concluded that the complete oxidative folding of LMW-GS is a late event, subsequent to GS inter-chain pairing.