Hydration water drives elastin's entropic elasticity.

Hydration water is the dominant entropic contributor to entropic recoil of a representative human tropoelastin elastomeric region during stretching, with stretching recruiting many waters into a low-entropy first layer.

• Why it matters: The molecular basis of elastin’s entropic recoil is unresolved, limiting mechanistic understanding of how elastin-like materials generate elasticity under deformation.
• What they did: Multi-microsecond all-atom simulations quantified protein conformational entropy, hydration-water entropy, and protein- and water-mediated interaction enthalpies while stretching a representative elastomeric region of human tropoelastin.
• The result: Protein conformational entropy decreases modestly overall, but hydration water provides the dominant unfavorable entropic term; enthalpic changes from disrupted intra-protein contacts and strengthened protein-water interactions largely compensate, supporting a hydration-coupled thermodynamic mechanism.

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