Sequential unfolding mechanisms of monomeric caspases

Area of Science:

• Biochemistry
• Evolutionary Biology
• Molecular Biology

Background:

• Caspases, essential proteases in cell development and apoptosis, exist as monomeric (initiator) or dimeric (effector) subfamilies.
• The evolutionary divergence of these subfamilies from a common ancestor and their distinct oligomeric states are not fully understood.
• Understanding caspase evolution is key to deciphering apoptosis regulation.

Approach:

• Examined the folding landscape of monomeric caspases from two coral species across a wide pH range (3-10.5).
• Utilized molecular dynamics simulations, limited proteolysis, and MALDI-TOF mass spectrometry to analyze protein stability and unfolding mechanisms.
• Compared evolutionary divergence times of coral and human caspases to infer evolutionary pressures.

Key Points:

• Coral caspases exhibit high stability (approx. 15 kcal mol^-1) near physiological pH and unfold through two intermediates.
• A pH-dependent conformational change, driven by conserved site titration, was observed in monomeric coral caspases.
• The small subunit of monomeric caspases is less stable and unfolds before the large subunit.

Conclusions:

• All caspases share a conserved folding landscape, indicating a common evolutionary origin.
• A conserved allosteric site allows for species-specific regulatory fine-tuning.
• The evolution of stable dimeric caspases may be linked to stabilizing the less stable small subunit.