Characterization of calmodulin-Fas death domain interaction: an integrated experimental and computational study

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• The Fas death receptor initiates apoptosis via the death-inducing signaling complex (DISC).
• Calmodulin (CaM) is known to interact with the Fas death domain (Fas DD), influencing DISC formation.
• Quantitative understanding of CaM-Fas interactions is crucial for developing therapeutic modulators.

Purpose of the Study:

• To quantitatively characterize the interaction between CaM and both wild-type Fas DD (Fas DD WT) and the V254N mutant Fas DD (Fas DD V254N).
• To elucidate the structural and thermodynamic basis of the V254N mutation's effect on CaM-Fas DD binding.
• To provide insights for designing novel strategies to modulate Fas-mediated apoptosis.

Main Methods:

• Isothermal titration calorimetry (ITC) to determine binding thermodynamics.
• Circular dichroism (CD) spectroscopy for secondary structure analysis.
• Molecular dynamics (MD) simulations to analyze conformational changes and interactions.

Main Results:

• ITC revealed an entropy-driven, endothermic interaction between CaM and both Fas DD WT and Fas DD V254N.
• The V254N mutation decreased the association constant (Ka) for CaM binding and slightly increased Gibbs free energy (ΔG°).
• MD simulations indicated no significant secondary structural changes but revealed alterations in conformational dynamics, hydrogen bonding, and electrostatic potentials within the CaM binding region.

Conclusions:

• The V254N mutation in Fas DD quantitatively alters CaM binding affinity and thermodynamics.
• Structural and dynamic changes, not secondary structure alterations, underlie the impaired CaM-Fas DD interaction.
• Findings offer a basis for developing targeted therapies to regulate CaM-Fas interactions and Fas-mediated apoptosis.