CHEMICAL SEQUENCE CONTROL OF BETA-SHEET ASSEMBLY IN MACROMOLECULAR CRYSTALS OF PERIODIC POLYPEPTIDES

A family of uniform periodic polypeptides has been prepared by bacteri al expression of the corresponding artificial genes, with the objectiv e of exploring the potential for control of supramolecular organizatio n in genetically engineered protein-based polymeric materials. The rep eating units of the polypeptides consist of oligomeric alanylglycine s equences interspersed with glutamic acid residues inserted at interval s of 8 to 14 amino acids. Crystallization of such materials from formi c acid produces beta-sheet structures in the solid state, as shown by vibrational spectroscopy, nuclear magnetic resonance spectroscopy, and wide-angle x-ray diffraction. The diffraction results, together with observations from electron microscopy, are consistent with the formati on of needle-shaped lamellar crystals whose thickness is controlled by the periodicity of the primary sequence. These results can be used to control solid-state structure in macromolecular materials.