Conformational analysis of the repeated sequence of glutelin‐2, a maize storage protein

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Abstract
The presence of repeated proline‐rich sequences constitutes a common trend in several cereal storage proteins. The protected hexapeptide Boc‐Val‐His‐Leu‐Pro‐Pro‐Pro‐OH (1), with the sequence of the repeated region of glutelin‐2 (28 kD) from maize, has been studied by proton and 13C NMR in D2O, DMSO‐d6, CDCl3 and CDCl3‐CD3OD at different temperatures. Spectra were assigned mainly by using 2D correlation techniques. The spectra in D2O and DMSO‐d6 suggest that peptide 1 has a random coil, all‐trans conformation. In CDCl3 1 presents a folded conformation, stabilized by hydrogen bonds, with one of the methyl groups of the valine residue situated over the histidine ring. In CDCl3‐CD3OD 1 is present as a mixture of different conformations. The spectral data are discussed taking as a reference the known conformation of polyproline.