PHYSICAL AND CHEMICAL MICROSTRUCTURE OF SPIDER DRAGLINE - A STUDY BY ANALYTICAL TRANSMISSION ELECTRON-MICROSCOPY

We report the first direct observations of the physical and chemical microstructure of spider dragline, revealed by analytical transmission electron microscopy. Individual crystallites were imaged within the amorphous matrix. They are irregularly shaped, approximately 70-100 nm in diameter, and uniformly distributed throughout the matrix. Electron diffraction determined their space group to be P2(1). The corresponding orthogonal cell has lattice parameters of a = 13.31 Angstrom (beta-sheet repeat), b = 9.44 Angstrom (interchain repeat within beta-sheets), and c = 20.88 Angstrom (repeat along polypeptide chain). Electron energy loss spectroscopy indicated compositional variations within the matrix, and between the crystallites and matrix. Most notably, calcium was found exclusively in the crystallites. Attempts to produce synthetic analogues of dragline, which exhibits an unparalleled combination of strength, stiffness, and toughness, cannot depend solely on duplicating the constituent proteins. The complex hierarchical microstructure of the natural material must be taken into account. (C) 1994 John Wiley & Sons, Inc.