Human RAD52 protein has extreme thermal stability.

Area of Science:

• Molecular Biology
• Protein Structure
• DNA Repair

Background:

• The RAD52 protein is crucial for homologous recombination, a key pathway for repairing DNA double-strand breaks.
• RAD52 monomers self-associate into ring structures, which can further assemble into higher-order complexes.
• These higher-order complexes are suggested to facilitate DNA end joining during repair.

Purpose of the Study:

• To investigate the thermal stability and self-association properties of wild-type RAD52 and a specific deletion mutant (RAD52(1--192)).
• To elucidate the structural basis for RAD52's stability and its role in DNA repair mechanisms.

Main Methods:

• Differential scanning calorimetry (DSC) was employed to analyze the thermal transitions and melting temperatures of RAD52.
• Dynamic light scattering (DLS) was used to study the effect of temperature and protein concentration on RAD52 self-association.
• A four-state hypothetical model was developed to interpret the thermal denaturation profile of wild-type RAD52.

Main Results:

• Wild-type RAD52 exhibited three thermal transitions (38.8°C, 73.1°C, 115.2°C), while the RAD52(1--192) mutant showed only two (47.6°C, 100.9°C).
• Transition A (38.8°C) was attributed to the dissociation of higher-order RAD52 complexes, transition B (73.1°C) to ring disruption, and transition C (115.2°C) to complete unfolding.
• Higher-order RAD52 complexes demonstrated stability at physiological temperatures in vitro.

Conclusions:

• The ring-shaped quaternary structure and higher-order complex formation of RAD52 contribute significantly to its remarkable thermal stability.
• These stable higher-order structures are likely important for RAD52's function in DNA double-strand break repair at physiological conditions.