DNA repair in antibody somatic hypermutation

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Somatic hypermutation (SHM) is essential for generating high-affinity antibodies.
• SHM involves DNA lesions initiated by activation-induced cytidine deaminase (AID) and subsequent repair.
• Repair mechanisms utilize DNA replication and repair factors, including mismatch repair (MMR) proteins and translesion DNA synthesis (TLS) polymerases.

Purpose of the Study:

• To integrate existing in vivo and in vitro findings on SHM.
• To discuss an integrated mechanistic model of SHM.

Main Methods:

• Review and contextualization of existing research findings.
• Mechanistic modeling of the SHM process.

Main Results:

• Activation-induced cytidine deaminase (AID) and specific TLS polymerases (pol theta, pol zeta, pol eta) are induced in B cells.
• These factors, along with MMR proteins, may form a multimolecular complex called a "mutasome" at DNA lesion sites.
• A "polymerase switch" occurs, replacing high-fidelity polymerases with error-prone TLS polymerases for mutation introduction during repair.

Conclusions:

• The mutasome model provides a framework for understanding SHM mechanisms.
• The polymerase switch is a critical event in generating antibody diversity through SHM.