Partial deuteration probing structural changes in supercontracted spider silk

Polarized IR-spectroscopic and mechanical measurements are combined to analyse the conformational changes in hydrogenated and partially deuterated major ampullate spider silk of Nephila edulis. Special attention is given to supercontraction and to the case where the latter is hindered by mechanical constraints. The determination of the molecular order parameters of the different moieties proves that the amide hydrogen exchange is a selective process, taking place at the surface of β-sheet nanocrystals, implying that these regions are accessible by water. The mechanical properties are changing dramatically when the fiber is wet (“supercontraction”) due to the fact that the pre-stress of the chains interconnecting the nanocrystals is irreversibly released. In course of this a novel network of H-bonds is formed, a process which can be suppressed if supercontraction is hindered.