Increased protein backbone conformational entropy upon hydrophobic ligand binding

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Hydrophobic interactions are crucial for protein-ligand binding.
• However, entropic penalties from association can limit binding affinity for small ligands.
• Alternative stabilization mechanisms are needed to understand these interactions.

Purpose of the Study:

• To investigate the role of protein flexibility and conformational entropy in stabilizing protein-ligand complexes.
• To explore binding mechanisms for small hydrophobic ligands where hydrophobic effects alone are insufficient.
• To determine if increased protein flexibility contributes to the binding of mouse pheromones.

Main Methods:

• Utilized Nuclear Magnetic Resonance (NMR) relaxation experiments.
• Studied the interaction between mouse major urinary protein (MUP) and a hydrophobic mouse pheromone (2-sec-butyl-4,5-dihydrothiazole).
• Analyzed changes in protein backbone flexibility and conformational entropy upon ligand binding.

Main Results:

• NMR data revealed increased backbone flexibility in MUP after binding the pheromone.
• This increased flexibility corresponds to a significant rise in the protein's conformational entropy.
• The entropic contribution to binding is substantial, comparable to other free energy contributions.

Conclusions:

• Increased protein backbone conformational entropy is a key factor in stabilizing protein-pheromone complexes.
• This mechanism, driven by enhanced flexibility, likely promotes the binding of very small hydrophobic ligands to macromolecules.
• This finding offers a broader perspective on molecular recognition beyond purely hydrophobic effects.