Recombinant Human APEX2 (DNA-(apurinic or apyrimidinic site) endonuclease 2) fragment (residues 1-334) is a high-purity protein designed for structural and biochemical studies. This stable and soluble unit retains key enzymatic activities, including weak AP endonuclease function, 3'-5' exonuclease, and 3'-phosphodiesterase capabilities, making it ideal for DNA repair research and enzyme characterization.

DNA-(apurinic or apyrimidinic site) endonuclease 2 (APEX2), encoded by the APEX2 gene in Homo sapiens, is a multifunctional enzyme central to the base excision repair (BER) pathway. It initiates repair of apurinic/apyrimidinic (AP) sites in DNA by hydrolytically cleaving the phosphodiester backbone adjacent to oxidative or alkylating damage, generating single-strand breaks with 5'-deoxyribose phosphate and 3'-hydroxyl ends. APEX2 also exhibits 3'-5' exonuclease activity, preferentially removing mismatched nucleotides from 3'-recessed heteroduplex DNA, blunt-ended substrates, and single-nucleotide gaps, along with 3'-phosphodiesterase activity to eliminate 3'-damaged termini caused by oxidative agents. In the nucleus, it operates in a PCNA-dependent BER mechanism, aids in reversing blocked 3' DNA ends to facilitate DNA synthesis, and is critical for somatic hypermutation and class switch recombination of immunoglobulin genes. Additionally, APEX2 supports proper cell cycle progression in proliferating lymphocytes. Subcellularly, it localizes to the nucleus, cytoplasm, and mitochondria, and redistributes with PCNA into nuclear foci upon oxidative DNA damage, underscoring its role in genomic stability and cellular defense.