Affiliation: | (1) European Synchrotron Radiation Facility, BP 220, 38043 Cedex Grenoble, France;(2) Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK |
Abstract: | The mechanical properties of spider dragline fibres are altered by CO2 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 CO2 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 -sheet domains containing nanofibrils, which reinforce a network of protein chains. The protein network absorbs water, leaving the nanofibrils unaffected. A continuous flow of CO2 results in a co-extrusion of a dragline thread and an isotropic silk fraction, which probably has a glycine-rich sequence. Long CO2 exposure reduces the axial alignment of nanofibrils, presumably due to a partial destruction of the amorphous network. |