Elastomeric proteins are characterized by their large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Motivated by their unique mechanical properties, there has been tremendous research in understanding and manipulating elastomeric polypeptides, with most work conducted on the elastin but more recent work on an expanded set of polypeptide elastomers. The literature data and analyses  affirm that components of elastin, and purified elastin fiber itself contain dynamic, non-random, regularly repeating structures that exhibit dominantly entropic elasticity by means of a damping of internal chain dynamics on extension. Tatham and coworkers have shown that the elastic modulus of HMW wheat gluten subunits crosslinked by γ-irradiation, similar to that of the crosslinked elastin polypentapeptide poly(VPGVG). Wheat glutenin is the main elastomeric protein in plants. The high molecular weight (HMW) subunits of wheat gluten are seed storage proteins, for storage of essential nutrients such as carbon, nitrogen and sulfur for growth of seedlings. The hexa-amino-acid repeats PGQGQQ and the nona-amino-acid repeats GYYPTSPQQ in the protein are considered to be mainly responsible for the elasticity of wheat gluten. Four opioid peptides were isolated from the enzymatic digest of wheat gluten. Their structures were GYYP, GYYPT, YGGW, and YGGWL, which were named gluten exorphin A4, A5, B4, and B5 respectively. The gluten exorphin A4 sequence was found at 21 sites in the primary structure of the high molecular weight glutenin and was highly specific for δ-receptors. It is worth mentioning that the proline containing peptides are resistant to cellular peptidases, and that cis/trans isomerization of the Xaa-Pro imidic bonds introduce steric interactions between the pyrrolidine ring δ-position and the preceding residue. The structure of GEA is unique in that, unlike most opioid peptides which have a Tyr in their N-terminus, GEA has a Gly in N-terminus (essential for opioid activity) and two continuous Tyr residues. In our work on synthetic opioid peptides  we studied conformational behavior in solution of conventionally protected gluten exorphinssequences. These products have been synthesized, purified, and then analyzed by CD and NMR spectroscopy. The work has clearly revealed the presence of folded conformations such as type II β-turn. Here we present preliminary results on conformational behavior of polymerizable subunits in which GEA4 β-turn act as spacer between two hydrophobic, extend segments having high propensity to form β-sheet.
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