NONPERIODIC LATTICE CRYSTALS IN THE HIERARCHICAL MICROSTRUCTURE OF SPIDER (MAJOR AMPULLATE) SILK

A commonly adopted model for the microstructure of Nephila clavipes ma jor ampullate silk (MAS) is similar to that used for Bombyx mori (silk worm) silk: a simple composite wherein discrete, essentially perfect c rystals are dispersed throughout an amorphous protein matrix. However, inconsistencies arise when researchers using complementary microstruc tural characterisation techniques attempt to explain their results wit hin that framework. We present here the findings of our parallel studi es in x-ray diffraction, electron microscopy, and molecular modeling. These results, combined with other data gleaned from the literature, l ead us to propose a revised description of the spider silk microstruct ure. The new model recognizes that the 70-500 nm sized ordered regions in MAS cannot be constructed from a simple motif of repeating monomer s, and develops the concept of non-periodic lattice (NPL) crystals to characterize these structures. The local composition, symmetry, and pe rfection of order vary over distances that are small compared to the s ize of an NPL crystal. (C) 1997 John Wiley & Sons, Inc.