Are natural protein networks similar to synthetic elastomeric networks? Structural implications of the characteristic pentapeptide repeat from the elastic protein network of wool

Abstract

Abstract The elasticity of the cross-linked matrix of wool fibers is not well understood. The primary structure of high sulfur proteins of the matrix is known to be dominated by the pentapeptide repeat CysGln2Pro3Thr4Cys5. The linear proteins containing the repeat are cross-linked by multiple CysCys disulfide bonds to form an elastic network. The existing hypothesis proposes that the disulfide bonds are formed predominantly between Cys1 and Cys5 of the same repeat, which is facilitated by the tight turn induced by the repeat. To elucidate the structural implications of the repeat, we applied solution 1H NMR to model peptides containing the repeat and also dynamic light scattering and electron microscopy to the polymeric products of their oxidation. The NMR measurements revealed that the repeat in the model peptides does not induce tight turns (water, DMSO). The NOE patterns indicate that to form the Cys1Cys5 intra-repeat disulfide bond, the Gln2-Pro3 peptide bond of the repeat changes its configuration from trans to cis. A substantial energy barrier associated with this transition should decrease the propensity of the repeat for the formation of the Cys1Cys5 bonds. The NMR measurements in DMSO-d6 revealed that for the repeat with a cycle closed by the Cys1Cys5 bond, a significant population of the conformations adopt a rare type VIa tight turn with cis-Pro3 in position i +2 of the turn. These results suggest that a modified model of the matrix is needed and that the nature of elasticity of the cross-linked polypeptide network from wool fiber might be similar to that of synthetic polymer networks.