Molecular structures and interactions of repetitive peptides based on wheat glutenin subunits depend on chain length

Synthetic and recombinant peptide models of the central repetitive domain of the high molecular weight subunits of wheat glutenin with different numbers of the consensus repeat motifs PGQGQQ + GYYPTSLQQ (21, 45, 110, and 203 residues long) and a recombinant 58,000-Da relative molecular mass (M(r) 58,000) repetitive peptide from a single subunit (1Dx5) are studied using Fourier transform IR spectroscopy. The spectra of the dry peptides are very similar; at low water contents (<76% relative humidity) there is an increase in beta-sheet structures in all peptides. However, on further hydration the content of beta sheets decrease and more beta turns are observed. The changes during the second step of hydration are very marked in the 21 and 45 residue peptides, but they are less apparent in the longer perfect repeat peptides. In the 110 and 203 residue peptides hydration results in increased contents of intermolecular beta-sheets and less beta-turn formation. In contrast, the beta-turn content of the M(r) 58,000 peptide increases during the second hydration step. The decreased extent of structure changes with increasing chain length indicates that cumulative intermolecular interactions, in particular hydrogen bonds, are an important factor in determining the structures in the solid state. The regularity of the perfect repeat sequences in the 21, 45, 110, and 203 residue peptides may favor the formation of larger stretches of intermolecular beta sheets. In contrast, the M(r) 58,000 peptide contains imperfect repeats (in common with native glutenin subunits), which may limit its ability to form intermolecular beta sheets.