Molecular Dynamics Simulations to Explore the Structure and Rheological Properties of Normal and Hyperconcentrated...

Area of Science:

• Biophysics
• Computational Biology
• Materials Science

Background:

• Airway mucus is crucial for respiratory health, but its dysfunction is implicated in diseases like cystic fibrosis.
• Mucin MUC5B is the primary gel-forming protein in airway mucus.
• Cystic fibrosis is associated with increased mucus concentration and the formation of dense mucus flakes.

Purpose of the Study:

• To develop the first molecular dynamics model of airway mucus based on MUC5B.
• To test the hypothesis that increased mucin concentration alone drives the formation of mucus flakes.
• To elucidate the biophysical mechanisms underlying mucus structural changes in cystic fibrosis.

Main Methods:

• Developed a molecular dynamics model of MUC5B using LAMMPS.
• Simulated MUC5B interactions at varying concentrations (1.5 and 5 mg/mL) with 9 nm spatial and 1 ns temporal resolution.
• Analyzed changes in domain proximity and interaction strengths.

Main Results:

• The model successfully replicated the formation of dense mucus flakes at higher concentrations.
• A 3.33-fold increase in MUC5B concentration (from 1.5 to 5 mg/mL) was sufficient to induce structural changes.
• Increased concentration led to closer proximity of MUC5B domains, amplifying hydrophobic and electrostatic interactions.

Conclusions:

• Increased mucin concentration is a sufficient driver for the formation of dense mucus flakes in airway mucus.
• The biophysical model provides a mechanistic explanation for mucus alterations in cystic fibrosis.
• This work offers insights into mucus rheology and potential therapeutic targets.