P. R. Shewry

Conformational studies of synthetic peptides corresponding to the repetitive regions of the high molecular weight (HMW) glutenin subunits of wheat.

Circular dichroism and Fourier transform infrared spectra of three synthetic peptides based on the repeat motifs of the HMW subunits of glutenin showed that they formed β-turns when dissolved in trifluoroethanol, a solvent that favours ordered structures stabilized by hydrogen bonds. Peptide 1, based on the hexapeptide repeat motif, was predicted to form a type II β-turn, while peptides 2 and 3 (which span the functions between hexapeptide and nonapeptide motifs) were predicted to form overlapping turns of types II and I/III. These predictions are consistent with the structures determined in trifluoroethanol. In contrast all three peptides appeared to have unordered structures when dissolved in H 2 O or D 2 O. These results are discussed in relation to the conformations of the HMW subunits.

Molecular structures and interactions of repetitive peptides based on HMW subunit 1Dx5

A characteristic feature of high molecular weight (HMW) subunits, as with many gluten proteins, is their large repetitive central domain. This consists of tandem and interspersed repeats based on two or three consensus motifs: a nonapeptide (Gly . T yr .T yr .Pro .Thr . S er .Pro/Leu. Gln. Gln), a hexapeptide (Pro .Gly . Gln. Gly . Gln. Gln) and, in the x-type subunits only, a tripeptide (Gly.Gln.Gln). Secondary structure prediction and spectroscopic studies of purified HMW subunits and short synthetic peptides based on the consensus repeat motifs have indicated that in solution the repetitive domain forms a loose spiral consisting of regularly repeated preverse turns’”. In the solid state numerous non-covalent intermolecular interactions exist. We have used Fourier-transform infrared spectroscopy to study perfect repeat peptides with different lengths in order to understand how this affects the molecular structures.