Self-assembly of recombinant human elastin polypeptides with potential for use in biomaterials applications

Elastin is an extracellular matrix protein found in a number of tissues, including the large arteries such as the aorta, imparting the characteristics of extensibility and elastic recoil. Once laid down in tissues, polymeric elastin is not subject to turnover but is able to sustain its mechanical resilience through billions of cycles of extension and recoil. The process of ordered assembly of elastin into its extracellular, polymeric form remains one of the least well-understood steps in the biosynthesis of elastin. During this step, side chains of lysine residues in elastin monomers must be oxidatively deaminated and brought into juxtaposition in preparation for crosslinking. In vivo, several factors have been proposed to contribute to the alignment of elastin monomers in the formation of polymeric elastin, including a microfibrillar scaffold and a cell surface elastin binding protein.; We have used a series of small, recombinant polypeptides based on sequences of human elastin to investigate the roles of various hydrophobic domains in promoting self-aggregation, and to determine whether this self-aggregation facilitates specific alignment of elastin polypeptides allowing crosslink formation at lysine residues. Our results demonstrate that polypeptides with as few as three hydrophobic and two crosslinking domains are able to self-aggregate into fibrillar structures essentially identical in appearance to those formed by the full-length elastin monomer, tropoelastin. Moreover, oxidation of lysine residues following aggregation, using a simple oxidizing agent (pyrroloquinoline quinone), results in spontaneous formation of lysine-derived covalent crosslinks between polypeptides, including desmosine and isodesmosine. Fabrication of these covalently crosslinked elastin polypeptides into membrane structures has also allowed assessment of their physical properties. Such membranes possess an elastic modulus, and extensibility and recoil properties similar to those of native insoluble elastin.; These results strongly support the view that, independent of the influences of other factors, monomers of elastin possess an intrinsic ability to organize themselves into polymeric structures, aligning lysine residues for covalent crosslinking and forming matrices with elastomeric properties. Understanding the basis of the self-organizational ability of elastin-based polypeptides may provide important clues for the general design of self-assembling biomaterials.