Protein Folding accompanied by disulfide bond formation drives glutenin polymerization into multidimensional gluten networks

Abstract

Wheat flour dough, which is routinely used to make bread, pasta and noodles, can be stretched several thousand-fold without rupture. The molecular basis of this extraordinary property arises due to the ability to crosslink glutenin subunits, the major constituent of dough, into linear and branched elastic networks. The mechanism by which the glutenin subunits self-assemble and polymerize is unknown. Here, we show, using mass spectrometry, confocal imaging and molecular dynamics simulations that structuring of two hydrophobic residues, phenylalanine and tyrosine, in the core region of the monomeric glutenin 1Dx5 N-terminal domain (1Dx5-NTD) initiates inter molecular interactions and network formation. Upon folding of monomeric 1Dx5-NTD, two cysteine residues (Cys10 and Cys40) form an intramolecular disulfide bond and poises the third cysteine (Cys25) to engage in inter molecular crosslink with other glutenin subunits. Propagation of such a disulfide linkage pattern results in the formation of a cohesive linear gluten network. In alternate pathways, crosslinking of Cys10 with Cys25 with a third glutenin subunit results in the creation of a junction, which drives the formation of a three-dimensional network. The disulfide patterns in the networks accord well with the measured chemical reactivity of each cysteine residue and the solvent accessibility of the associated side chains during 1Dx5-NTD interactions. Our study shows that the diversity in the folding of a single glutenin subunit that exposes the third cysteine to the solvent is the key event that initiates polymerization and directs the formation of networks with differing architecture. Significance statementGlutenin proteins polymerize to form intricate molecular networks that support the expansion of dough by several thousand-fold. Although network formation occurs spontaneously, the polymerization mechanism is unknown. There are multiple cysteine residues in glutenin that can form intra and intermolecular disulfide bonds. Multiple experimental techniques and molecular dynamics simulations are used to show that folding of glutenin, initiated by two hydrophobic residues, exposes cysteines that are poised to form intermolecular disulfide bonds. The disulfide crosslinking pattern, determined by the initial folding process, dictates the creation of a linear or branched network. The study demonstrates that the propensity to form linear or branched networks is encoded by the diversity of the disulfide patterns created at the level of monomeric folding.