Validation of the "Stoichiometric Hydration Ice-Bridge Model" Provides Method To Predict Protein Folding Energetics.

Area of Science:

• Biophysics
• Structural Biology
• Macromolecular Science

Background:

• Macromolecular hydration is crucial for biological functions like cellular pore regulation and protein conformational changes.
• Understanding the energetics of protein-bound water is essential for deciphering these life-critical processes.

Purpose of the Study:

• To quantify the energetics of collagen hydration by investigating ice-bridge formation on protein backbones.
• To provide a molecular definition of protein-bound water through stoichiometric hydration ice-bridge counts (SHIM theory).

Main Methods:

• Utilized rat tail tendon collagen due to its high in vitro stability and 100% occupancy of ice nucleation sites.
• Employed SHIM theory to calculate enthalpy and entropy of collagen melting based on ice-bridge properties.
• Investigated the effect of acetate ions on collagen hydration and entropy.

Main Results:

• Calculated the specific enthalpy of native collagen melting (ΔHm = 70.31 J/g-collagen) using SHIM theory, aligning with experimental data.
• Determined that 100% of collagen's entropy of melting originates from restricted water mobility in the first monolayer.
• Observed an increase in entropy upon acetate ion penetration, indicating altered hydration slurry formation.

Conclusions:

• Established a molecular definition for protein-bound water and the energetic basis of macromolecular shape changes.
• The SHIM theory provides a calculational framework for water interactions with various macromolecules, including DNA, RNA, and cellulose.
• This research offers insights into the role of glucose in collagen hydration changes relevant to diabetes complications.