Research: Elastin Materials
Dynamics in Elastin Assembly and Function
A newer project in the lab involves the design of elastin-based materials. Elastin is the most famous member of a class of intrinsically disordered hydrophobic proteins that self-assemble into elastic materials. Elastin makes up blood vessel walls and drives the elastic recoil necessary for cardiac function. Incredibly, it undergoes more than three billion recoil cycles during your lifetime without being repaired or replaced. Despite over 50 years of biophysical analysis of this protein-based entropic spring, the mechanism and structural engineering parameters of elastins are not understood. Elastin is unique in that the atomic-level structure and dynamics of a single protein translate directly into macroscopic material properties.
With NSF support, we have designed simplified but fully functional artificial elastin proteins by sequence averaging the hydrophobic domains — creating a simplified elastin composed of seven identical hydrophobic and crosslinking domains which retains the solution properties of natural elastin, including coacervation, material formation and temperature dependent contraction. These are allowing us to look at the structure and dynamics of a functional elastin protein in all four states — soluble, coacervated, entangled solid and crosslinked material — with atomic resolution using solution and solid state NMR.
(Left) Temperature-dependent compaction of minielastin variants. (Right) Temperature dependence of the NMR chemical shifts in minielastin 24x’.
Thus far there are three significant findings based on our work:
1. The recoil force is driven by the hydrophobic effect and not configurational entropy as evinced by NMR dynamics measurements we have performed on stretched and relaxed elastin fibers in the absence and presence of chaotropes and kosmotropes.
2. The individual soluble domains shrink with increasing temperature to a degree that closely approximates the volumetric shrinkage of the fully assembled material. We have shown that we can tune this property by altering the size of the hydrophobic domains, suggesting that we can make tunable elastin materials.
3. Unlike most disordered proteins that coacervate, elastin coacervates harden into an insoluble form over time even without the enzymatic crosslinking that occurs during natural elastogenesis.
Solid-state NMR determination of the order parameters in Bovine elastin
This work is being done together with the solid state NMR expert Richard Wittebort at the University of Louisville and coacervation expert Shana Elbaum-Garfinkle of the CUNY ASRC. We have also started a new collaboration with the elastocaloric materials expert Karl Sandeman at Brooklyn College, making energy storage materials with these proteins.