Lattice deformation and thermal stability of crystals in spider silk.
The X-ray diffraction of dragline silks, produced by Nephila and Cyrtophora spiders, were measured by synchrotron radiation in their original states or in situ during stretching and heating. Nephila pilipes spiders construct a two-dimensional orb web that must be rebuilt in one or 2 days, but Cyrtophora spiders form a three-dimensional tent web that can exist for several weeks in a tropical forest. Diffraction patterns of N. pilipes and Cyrtophora draglines resemble each other. Crystals of two kinds are identified in these draglines; one is aligned parallel to the silk direction and another is less oriented. The less oriented crystal in Cyrtophora dragline is aligned better than that in N. pilipes dragline, which generates about three times stronger diffract intensity. Crystals in N. pilipes and C. moluccensis dragline silks have remarkable thermal stability. Equatorial reflections remain undiminished until 350 and 450 degrees C for N. pilipes and C. moluccensis, respectively. In contrast, the meridional reflections S and (002), which are parallel to the silk thread, disappear at a temperature less than 100 degrees C for C. moluccensis but remain for Nephila up to 100 degrees C. Meridional reflections S and (002) shift to a smaller angle during stretching, whereas equatorial reflections remain constant in a range 1.0-1.3 times the original length. The position of the S reflection shifts rapidly in the first 10% of elongation from the original length but remains constant during subsequent stretching, whereas the (002) reflection shifts rapidly during the first 5% elongation from the original length and continues to shift subsequently. In contrast, the features of N. pilipes dragline alter insignificantly during stretching. Examination of the composition of amino acids of the draglines of N. pilipes and C. moluccensis indicates that a dragline of N. pilipes contains more glycine, but much less alanine, than that of C. moluccensis.
Sheu
Hwo-Shuenn
HS
National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan. hsheu@nsrrc.org.tw
Phyu
Khin Win
KW
Jean
Yuch-Cheng
YC
Chiang
Yung-Ping
YP
Tso
I-Min
IM
Wu
Hsuan-Chen
HC
Yang
Jen-Chang
JC
Ferng
Shyue-Lih
SL
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D003460:Crystallization; D047011:Silk / Q000737:chemistry*; D013045:Species Specificity; D013112:Spiders / Q000737:chemistry*; D013696:Temperature; D014961:X-Ray Diffraction
D000596:Amino Acids; D047011:Silk