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 m icrostructure of spider dragline, revealed by analytical transmission electron microscopy. Individual crystallites were imaged within the am orphous matrix. They are irregularly shaped, approximately 70-100 nm i n diameter, and uniformly distributed throughout the matrix. Electron diffraction determined their space group to be P2(1). The correspondin g orthogonal cell has lattice parameters of a = 13.31 Angstrom (beta-s heet repeat), b = 9.44 Angstrom (interchain repeat within beta-sheets) , and c = 20.88 Angstrom (repeat along polypeptide chain). Electron en ergy loss spectroscopy indicated compositional variations within the m atrix, and between the crystallites and matrix. Most notably, calcium was found exclusively in the crystallites. Attempts to produce synthet ic analogues of dragline, which exhibits an unparalleled combination o f strength, stiffness, and toughness, cannot depend solely on duplicat ing the constituent proteins. The complex hierarchical microstructure of the natural material must be taken into account. (C) 1994 John Wile y & Sons, Inc.