Highly Dynamic Anion-Quadrupole Networks in Proteins.

Area of Science:

• Computational chemistry
• Structural biology
• Protein dynamics

Background:

• Anion-quadrupole (anion-π) interactions involve negatively charged amino acid side chains (aspartate/glutamate) and aromatic side chains (phenylalanine).
• These interactions are crucial for protein stability but their dynamic nature is not fully understood.

Purpose of the Study:

• To computationally characterize the dynamics of anion-quadrupole interactions in the RmlC epimerase.
• To investigate the contribution of these interactions to protein stability and identify compensatory mechanisms.

Main Methods:

• Empirical force field-based molecular dynamics simulations.
• Analysis of anion-quadrupole pair and triplet formation.
• Double-mutant cycle analysis of thermal stability.

Main Results:

• Anion-quadrupole pairs and triplets are predicted to form dynamically during simulations.
• These interactions contribute significantly to protein stability (average -1.6 kcal/mol per pair).
• Observed anion-π interactions exhibit transient stability, alternating between 'on' and 'off' states.

Conclusions:

• Anion-quadrupole interactions play a dynamic role in maintaining protein structural stability and function.
• Proteins may compensate for transient loss of these interactions through hydration and other electrostatic interactions.
• Near-planar anion-quadrupole pairs can exist transiently, influencing the protein's non-bonded interaction network.