ARE NATURAL PROTEIN NETWORKS SIMILAR TO SYNTHETIC ELASTOMERIC NETWORKS - STRUCTURAL IMPLICATIONS OF THE CHARACTERISTIC PENTAPEPTIDE REPEAT FROM THE ELASTIC PROTEIN NETWORK OF WOOL

The elasticity of the cross-linked matrix of wool fibers is not well u nderstood The primary structure of high sulfur proteins of the matrix is known to be dominated by the pentapeptide repeat Cys(1)-Gln(2)-Pro( 3)-Thr(4)-Cys(5). 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 Cys(1) and Cys(5) of the same repeat, which is f acilitated by the tight turn induced by the repeat. To elucidate the s tructural implications of the repeat, we applied solution H-1 NMR to m odel 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 do es not induce tight turns (water, DMSO). The NOE patterns indicate tha t to form the Cys(1)-Cys(5) intra-repeat disulfide bond, the Gln(2)-Pr o(3) peptide bond of the repeat changes its configuration from trans t o cis. A substantial energy barrier associated with this transition sh ould decrease the propensity of the repeat for the formation of the Cy s(1)-Cys(5) bonds. The NMR measurements in DMSO-d(6) revealed that for the repeat with a cycle closed by the Cys(1)-Cys(5) bond, a significa nt population of the conformations adopt a rare type Via right turn wi th cis-Pro(3) in position i+2 of the rum. These results suggest that a modified model of the matrix is needed and that the nature of elastic ity of the cross-linked polypeptide network from wool fiber might be s imilar to that of synthetic polymer networks. Copyright (C) 1996 Elsev ier Science Ltd.