Influence of CO2 on the micro-structural properties of spider dragline silk: X-ray microdiffraction results.
Riekel C., Rössle M., Sapede D., Vollrath F.
The mechanical properties of spider dragline fibres are altered by CO(2) exposure under anaesthetizing conditions during the spinning process. In order to relate these macroscopic changes to a microscopic model, the extrusion of dragline silk was studied by synchrotron radiation microdiffraction. A brief exposure of a female Nephila senigalensis spider to CO(2 )results after an incubation time of less than 7 min in the extrusion of a thread (two fibres) swollen with water. The data are interpreted for a model of crystalline beta-sheet domains containing nanofibrils, which reinforce a network of protein chains. The protein network absorbs water, leaving the nanofibrils unaffected. A continuous flow of CO(2) results in a co-extrusion of a dragline thread and an isotropic silk fraction, which probably has a glycine-rich sequence. Long CO(2) exposure reduces the axial alignment of nanofibrils, presumably due to a partial destruction of the amorphous network.