NMR Study of Elastin's Elasticity Mechanism

Abstract

Elastin is the most abundant elastomer in nature. The recoil mechanism is believed to be entropically driven for which there re two molecular level theories. Recoil in one theory is a rubber-like mechanism in which the decrease in entropy with stretch is due to a decrease in conformational entropy from backbone ordering. The alternative is a decrease in solvent entropy with stretch from solvent ordering, i.e., the hydrophobic effect. Using a novel double quantum (2Q) pulse sequence in solid state NMR; water ordering at elastin fiber surface was studied quantitatively. We find that water is weakly oriented at the Elastin-water surface when the fiber is relaxed and stretching the fiber or increasing the temperature significantly increases the 2Q signal, i.e., increases the ordered water fraction. Furthermore, the 2Q signal decreases with the addition of high molecular weight polyethylene glycol (20kDa or 6kDa PEG) that is known to precipitate proteins and decrease their hydration in solution. We believe PEG causes less water to be available on the fibers surface and thus less ordered water. Also, this is likely the reason why the fibers become less flexible. Our preliminary results in both water and high molecular weight PEG experiments directly correlate the recoil mechanism with the hydrophobic effect.