Elastin recoil is driven by the hydrophobic effect

Area of Science:

• Biophysics
• Materials Science
• Biochemistry

Background:

• Elastin is a vital extracellular matrix protein in vertebrates, providing elasticity to tissues like arteries, lungs, and skin.
• Its remarkable resilience, enduring billions of cycles without replacement, is key to tissue function and longevity.
• The long-standing debate over elastin's recoil mechanism, whether entropic or otherwise, has persisted for over five decades.

Purpose of the Study:

• To elucidate the primary driving force behind elastin's elastic recoil mechanism.
• To investigate the role of water ordering and thermodynamic properties in elastin's function.
• To challenge the prevailing entropic recoil theory and propose an alternative mechanism.

Main Methods:

• Utilized a combined Nuclear Magnetic Resonance (NMR) and thermomechanical study.
• Observed water ordering at the solvent:protein interface using double quantum 2H NMR as a function of stretch.
• Conducted extensive thermodynamic analysis by measuring elastin length and volume under varying force, temperature, and solvent conditions.

Main Results:

• Demonstrated that water ordering at the solvent:protein interface increases proportionally with elastin stretching.
• Observed increased heat capacity and decreased internal energy upon stretching, with heat released exceeding work performed.
• Thermodynamic signatures were altered by cosolvents that modify the hydrophobic effect, supporting its role.

Conclusions:

• The hydrophobic effect, not configurational entropy, is the primary driver of elastin recoil under physiological conditions.
• This mechanism explains elastin's exceptional resilience and resistance to hardening, unlike rubber.
• The hydrophobic effect-driven recoil is proposed as the fundamental origin of elastin's unique properties and longevity.