There is currently a considerable interest in dragline spider silk due to its exceptional mechanical qualities [1]. X-ray structural studies of silk have been limited to few spider species where sufficiently large quantities of spider silk could be obtained by the so-called forced silking technique [2]. ID13 has pioneered the development of single fibre diffraction techniques, which have allowed the collection of diffraction patterns from a variety of spider silks [3]. The development of artificial silk requires a detailed understanding of the structural processes occurring during the formation of the natural product. It is therefore of interest to apply the same in situ techniques, which have been developed for the study of extrusion processes of synthetic polymers, to extrusion from the living animal. Of course, given the size of a spider, an extreme miniaturisation of the setup was required.

Figure 1 shows the setup used for studying a Nephila senigalensis spider using a 10 µm sized beam at the ID13 beamline [4]. Forced silking can be maintained for several hours under these conditions and the spiders remain unharmed by this procedure. Figure 2 shows a typical scattering pattern obtained during the extrusion as recorded by a MAR CCD detector. The pattern reflects a mixture of small crystallites with the ß-poly(L-alanine) structure in an oriented, amorphous matrix. For the in situ extrusion of synthetic polymers, the influence of parameters such as the extrusion speed on the microstructure can be studied. Of particular interest in future studies will be to find out the extent to which this biopolymer production line is influenced by environmental parameters such as temperature etc. This opens a window into the study of a fascinating biophysical process.

References
[1] J.M. Gosline, M.E. DeMont, M.W. Denny, Endeavour, 10(1), 37-43 (1986).
[2] R.W. Work, P.D. Emerson, J. Arachnol., 10, 1-10 (1982).
[3] C. Riekel et al., Int. J. Mol. Biol., 24(2-3), 187-195 (1999).
[4] C. Riekel, M. Mueller, F. Vollrath, Macromolecules, 32(13), 4464-4466 (1999).

Authors
C. Riekel (a), M. Mueller (a), F. Vollrath (b,c).

(a) ESRF
(b) Department of Zoology, University of Aarhus (Denmark)
(c) Department of Zoology, University of Oxford (UK)