Synthesis and Assembly of Elastin and Elastin-Like Structural Proteins of the Extracellular Matrix

Research Synopsis

Elastin is the major structural protein of the large blood vessels, giving these tissues the physical properties of extensibility and elastic recoil which are essential for their physiological function. Our laboratory has had a long-standing interest in the biochemistry of elastin, it's synthesis and assembly in the extracellular matrix, its role in cardiovascular development and diseases such as atherosclerosis and hypertension and its functional and evolutionary relationship to other glycine-rich, elastin-like structural proteins in a variety of tissues and species.


Sequence, Structure, and Self-Assembly of Elastin
    To achieve the exceptional durability, structural integrity and elastomeric properties of the elastic matrix, monomers of elastin must be aligned into the appropriate architecture in the extracellular space and then covalently crosslinked into an extended polymer. How this ordered assembly of elastin monomers takes place is not well-understood. We have demonstrated that interactions between hydrophobic domains in the elastin monomers themselves play a role in their alignment and in the assembly of elastin polymers. We are particularly interested in understanding the relationship between the sequence and structure of elastin and it's functional properties, including both its ability to undergo this crucial first step of self-assembly and the mechanical properties of the final polymeric matrix formed from the protein.
    We are characterizing the self-assembly properties of recombinant polypeptides based on the sequence and domain structure of elastins and have shown not only that these simplified polypeptides can mimic the ability of elastin monomers to organize themselves into polymers through hydrophobic self-assembly , but also that these polymers can be stabilized by crosslinking into biomaterials with physical properties remarkably similar to those of the native polymeric elastin.


Phylogenetic Variations in Elastin Sequence, Structure and Self-Assembly
    A second approach to understanding sequence-structure-function relationships in elastin has involved an analysis of variations in sequence of both hydrophobic and crosslinking domains over a broad phylogenetic range. We have now extended the phylogenetic range of known elastin sequences to include teleost and more amphibian elastins. The results of these studies have also provided important new insights into the evolutionary history of elastin and suggested not only design features of the protein which are conserved across this broad range of species and are therefore likely important for it's fundamental properties of extension and recoil, but also sequence variants which may be determinants of variations in physical properties of elastic tissues between species.


Evolution of Elastin: Relationships to Other Glycine-Rich Matrix Proteins of Lower Vertebrates and Invertebrates.
    The evolutionary origins of elastin are obscure. While elastin is a major component of large arteries in virtually all species above agnathans, the protein is absent from arterial tissues of agnathans such as lamprey and hagfish, as well as from invertebrates with a closed circulatory system. We and our colleagues have shown, however, that elastin-like proteins form the major structural element of cartilaginous tissues in these lower vertebrates and invertebrates. We are characterizing the family of elastin-like proteins in lower vertebrate and invertebrate cartilage. To date we have cloned, sequenced and characterized a major elastin-like structural protein of lamprey skeletal cartilage, and are presently in the process of detailed characterization of several other members of this family of cartilage proteins.

Scanning electron micrograph of the surface of a biomaterial made from elastin polypeptides

Biomaterial made from elastin polypeptides mounted for determination of elastic properties

Mechanical properties of biomaterials made from elastin polypeptides: stress/strain curves for repeated cycles of loading and unloading

S. Vieth, C. M. Bellingham, F. W. Keeley, S. M. Hodge,  and D. Rousseau,
Microstructural and Tensile Properties of Elastin-based Polypeptides
Crosslinked with Genipin and Pyrroloquinoline Quinone, Biopolymers 85,
199-206, 2007.

J. T. Cirulis, C. M. Bellingham, E. C. Davis, D. Hubmacher, D. Reinhard, R.
P. Mecham and F. W. Keeley, Fibrillins, Fibulins and MAGP Modulate the
Kinetics and Morphology of In Vitro Self-Assembly of a Recombinant
Elastin-like Polypeptide, Biochemistry 47, 12601-12613, 2008.

M. Miao, R.J. Stahl, W. Reintsch, E. Davis and F. W. Keeley,
Characterization of an Unusual Tropoelastin with Truncated C-Terminus in
the Frog, Matrix Biology 28, 432-441, 2009.

L. D. Muiznieks, A. S. Weiss and F. W. Keeley.Strucutral Disorder and
Dynamics of Elastin, Canadian Journal of Biochemistry and Cell Biology,
Biochem. Cell Biol. 88, 239-250, 2010.

J. T. Cirulis and F. W. Keeley, Kinetics and Morphology of Self-assembly of
an Elastin-like Polypeptide Based on the Alternating Domain Arrangement of Human Tropoelastin, Biochemistry 49, 5726-5733, 2010

L. D. Muiznieks and F. W. Keeley, Proline Periodicity Modulates the
Self-Assembly Properties of Elastin-Like Polypeptides, J Biol Chem 285:
39779-39789, 2010.