The structural stability of the HIV-1 protease

Area of Science:

• Biochemistry and Biophysics
• Structural Biology
• Enzyme Kinetics and Thermodynamics

Background:

• HIV-1 protease inhibitors commonly target active sites or structural destabilization.
• Optimizing inhibitor design requires understanding protease stabilization energetics and critical regions.
• Previous studies lacked detailed energetic analysis of HIV-1 protease stabilization.

Purpose of the Study:

• To quantify the energetics of HIV-1 protease stabilization for the first time.
• To identify regions critical for protease stability and function.
• To evaluate the contributions of enthalpy, entropy, and heat capacity to stabilization.

Main Methods:

• High-sensitivity differential scanning calorimetry (DSC) was employed to measure stabilization energetics.
• Structure-based thermodynamic analysis was performed to map energy contributions.
• pH and concentration dependence of protease stability were investigated.

Main Results:

• Protease stability is pH- and concentration-dependent, with Gibbs energy of stabilization increasing at higher pH.
• The dimerization interface contributes the majority of stabilization energy, with specific "hot spot" residues (e.g., termini) being crucial.
• Flap regions exhibit marginal stability and are prone to local unfolding, potentially explaining inhibitor resistance mutations.

Conclusions:

• The dimerization interface is essential for HIV-1 protease stability; isolated subunits are unstable.
• Specific residues at the termini and active site base significantly contribute to subunit association.
• The flap region's inherent instability may be a key factor in developing drug resistance.