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A family of uniform periodic polypeptides has been prepared by bacterial expression of the corresponding artificial genes, with the objective of exploring the potential for control of supramolecular organization in genetically engineered protein-based polymeric materials. The repeating units of the polypeptides consist of oligomeric alanyl-glycine sequences interspersed with glutamic acid residues inserted at intervals of 8 to 14 amino acids. Crystallization of such materials from formic 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 formation 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.

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Solutions and melts of stiff ('rod-like') macromolecules often exhibit nematic liquid crystalline phases characterized by orientational, but not positional, molecular order. Smectic phases, in which macromolecular rods are organized into layers roughly perpendicular to the direction of molecular orientation, are rare, owing at least in part to the polydisperse nature (distribution of chain lengths) of polymers prepared by conventional polymerization processes. Bacterial methods for polypeptide synthesis, in which artificial genes encoding the polymer are expressed in bacterial vectors, offer the opportunity to make macromolecules with very well defined chain lengths. Here we show that a monodisperse derivative of poly(gamma-benzyl alpha,L-glutamate) prepared in this way shows smectic ordering in solution and in films. This result suggests that methods for preparing monodisperse polymers might provide access to new smectic phases with layer spacings that are susceptible to precise control on the scale of tens of nanometres.

Synthetic polymers have attained a dominant position in materials science and technology largely on the basis of their excellent physical and mechanical properties. The more subtle chemical and biological properties of natural polymers, especially of the proteins and nucleic acids, have been difficult to capture in synthetic macromolecular materials, in part because these properties arise from microstructural features that cannot be controlled in statistical polymerization processes. We describe herein the use of artificial genes to direct the synthesis of polymers of precisely controlled architecture, 1 in which biological functionsspecifically, the capacity to support attachment of vascular endothelial cellssis the primary object of the design. A long-term objective of this work is the development of improved materials for the regeneration, replacement or repair of vascular tissue.Surgical reconstruction of small-and medium-diameter blood vessels is exceedingly difficult. The material of choice for vascular reconstruction in the lower leg is autologous saphenous vein if it is available and healthy; unfortunately, the success rates for such reconstructive procedures are generally only about 70% after 5 years. 2 Poly(tetrafluoroethylene) and poly(ethylene terephthalate) have also been used for small-and medium-caliber grafts; however, patency rates for these materials are even lower than those for saphenous vein. 2b,3 Failure most often occurs through thrombosis and occlusion of the graft or through neointimal hyperplasia at the junction between the graft and the surrounding tissue. New materials are needed for the construction of improved vascular prosthetics.In an attempt to address this need, we report herein the preparation of artificial extracellular matrix proteins 4 comprising two kinds of elements: (i) a repeating unit structure (GVPGI) x 5 related to mammalian elastin and (ii) a cell-binding domain (designated CS5) derived from the natural extracellular matrix protein fibronectin. 6 Our choice of the elastin-like repeating unit was based on the extensive work of Urry and co-workers 7 on the family of polypentapeptides represented as -(GVPGZ) x -, where Z can be any of a wide variety of amino acid residues; the specific choice of Z ) I was dictated by the anticipated thermal transition behavior of the polymer (vide infra). Urry has suggested the use of elastinlike polypeptides in a vascular graft design in which the intimal layer bears peptide signals for endothelial cell attachment. 8 The results reported here relate directly to this proposal, in that the CS5 region of fibronectin contains the REDV sequence previously shown to support attachment and spreading of endothelial cells, but not smooth muscle cells or platelets, on artificial surfaces. 9 We describe here the microbial expression of artificial extracellular matrix proteins carrying CS5 domains, and we demonstrate that such proteins do in fact support attachment and spreading of vascular endothelial cells.The target polymers can be represented b...