A RECOMBINANT PROTEIN OF 2 HIGH-MOLECULAR-WEIGHT GLUTENINS ALTERS GLUTEN POLYMER FORMATION IN TRANSGENIC WHEAT

Wheat high molecular weight glutenin subunits (HMW-GS) are the most im portant determinants of its superiority for making leavened bread, Fol lowing synthesis, these proteins are sequestered into the endoplasmic reticulum and assemble into extremely large elastic polymers, linked b y noncovalent and intermolecular disulfide bonds. To study the structu ral requirements for the assembly of HMW-GS, we have expressed in tran sgenic wheat a recombinant protein between two cognate x- and y-type s ubunits, In contrast to the natural polymerized x- and y-type HMW-GS, a significant amount of the recombinant subunit remained monomeric, No nreducing SDS-polyacrylamide gel electrophoresis, coupled with limited proteolysis, showed that the monomeric form of the recombinant subuni t contained an unusual intramolecular disulfide bond, linking an N-ter minal cysteine to the single C-terminal cysteine residue, In addition, sucrose gradient analysis revealed that this intramolecular disulfide bond impeded the ability of the recombinant subunit to assemble into polymers. Despite of its altered assembly, a notable amount of the ove rexpressed recombinant subunit was also present in glutenin polymers, Moreover, its presence significantly altered the subunit composition o f the polymer, Our results show that it is possible to modify gluten a ssembly and properties by expressing recombinant HMW-GS in transgenic wheat, and have a major implication for the improvement of wheat bread making quality.