Nanofibrillar structure and molecular mobility in spider dragline silk
Sapede D., Seydel T., Forsyth VT., Koza MM., Schweins R., Vollrath F., Riekel C.
Nephila edulis dragline silk has been investigated by elastic and quasielastic neutron scattering techniques. The data support a three-phase model of nanofibrils, composed of crystalline and short-range order domains, which are embedded in an amorphous matrix of random protein chains. A meridional superlattice peak in D2O-exchanged silk is tentatively assigned to a smectic β-sheet structure in the short-range order domains. Water is absorbed preferentially by the amorphous matrix. The onset of molecular mobility in hydrated silk at about 200 K is attributed to water molecules, which move on the picosecond time scale. Coexisting slower motions on the nanosecond time scale are possibly due to polymer chain dynamics. Native silk at rest appears to behave similar to a glass below 300 K. © 2005 American Chemical Society.