Expression and purification of active mouse and human NEIL3 proteins

Endonuclease VIII-like 3 (Neil3) is one of the five DNA glycosylases found in mammals that recognize and remove oxidized bases, and initiate the base excision repair (BER) pathway. Previous attempts to express and purify the mouse and human orthologs of Neil3 in their active form have not been successful. Here we report the construction of bicistronic expression vectors for expressing in Escherichia coli the full-length mouse Neil3 (MmuNeil3), its glycosylase domain (MmuNeil3 Delta 324), as well as the glycosylase domain of human Neil3 (NEIL3 Delta 324). The purified Neil3 proteins are all active, and NEIL3 Delta 324 exhibits similar glycosylase/lyase activity as MmuNeil3 Delta 324 on both single-stranded and double-stranded substrates containing thymine glycol (Tg), spiroiminodihydantoin (Sp) or an abasic site (AP). We show that N-terminal initiator methionine processing is critical for the activity of both mouse and human Neil3 proteins. Co-expressing an E. coli methionine aminopeptidase (EcoMap) Y168A variant with MmuNeiI3, MmuNeil3 Delta 324 and Neil3 Delta 324 improves the N-terminal methionine processing and increases the percentage of active Neil3 proteins in the preparation. The purified Neil3 proteins are suitable for biochemical, structural and functional studies. (c) 2012 Elsevier Inc. All rights reserved.