STRUCTURE CHARACTERIZATION OF THE CENTRAL REPETITIVE DOMAIN OF HIGH-MOLECULAR-WEIGHT GLUTEN PROTEINS .2. CHARACTERIZATION IN SOLUTION AND IN THE DRY STATE

The structure of the central repetitive domain of high molecular weigh t (HMW) wheat gluten proteins was characterized in solution and in the dry state using HMW proteins Bx6 and Bx7 and a subcloned, bacterially expressed part of the repetitive domain of HMW Dx5. Model studies of the HMW consensus peptides PGQGQQ and GYYPTSPQQ formed the basis for t he data analysis (van Dijk AA et al., 1997, Protein Sci 6:637-648). In solution, the repetitive domain contained a continuous nonoverlapping series of both type I and type II beta-turns at positions predicted f rom the model studies; type II beta-turns occurred at QPGQ and QQGY se quences and type I beta-turns at YPTS and SPQQ. The subcloned part of the HMW Dx5 repetitive domain sometimes migrated as two bands on SDS-P AGE; we present evidence that this may be caused by a single amino aci d insertion that disturbs the regular structure of beta-turns. The typ e I beta-turns are lost when the protein is dried on a solid surface, probably by conversion to type II beta-turns. The homogeneous type II beta-turn distribution is compatible with the formation of a beta-spir al structure, which provides the protein with elastic properties. The beta-turns and thus the beta-spiral are stabilized by hydrogen bonds w ithin and between turns. Reformation of this hydrogen bonding network after, e.g., mechanical disruption may be important for the elastic pr operties of gluten proteins.