The reaction of serpins with proteinases involves important enthalpy changes

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Serpins (serine protease inhibitors) are crucial regulators of protease activity.
• Proteolytic inactivation of active serpins involves a conformational transition and increased stability.
• Understanding the thermodynamics of these transitions is key to comprehending serpin function.

Purpose of the Study:

• To investigate the thermodynamic changes associated with serpin inactivation via proteolytic cleavage.
• To compare the enthalpy changes during serpin inactivation versus inhibition.
• To elucidate the role of enthalpy changes in stabilizing proteases.

Main Methods:

• Microcalorimetry was employed to measure enthalpy changes (DeltaH) and heat capacity (DeltaC(p)()).
• Specific serpin-proteinase interactions were studied, including alpha(1)-proteinase inhibitor and antithrombin.
• Various proteases were used, such as Pseudomonas aeruginosa elastase, Staphylococcus aureus V8 proteinase, papain, and leukocyte elastase.

Main Results:

• Proteolytic inactivation of active serpins resulted in large enthalpy changes (DeltaH = -53 to -63 kcal mol(-1)).
• Serpin inhibition released significantly less heat (DeltaH = -20 to -31 kcal mol(-1)).
• A large negative heat capacity (DeltaC(p)() = -566 cal K(-1) mol(-1)) was observed for alpha(1)-proteinase inhibitor cleavage.

Conclusions:

• The structural transition upon serpin inactivation is thermodynamically distinct from inhibition.
• A substantial portion of the enthalpy change likely stabilizes the protease in an inactive conformation.
• These findings provide thermodynamic insights into the mechanism of serpin-mediated protease regulation.