Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) interacts with apurinic/apyrimidinic sites in DNA

Apurinic/apyrimidinic (AP) sites are some of the most frequent DNA damages and the key intermediates of base excision repair. Certain proteins can interact with the deoxyribose of the AP site to form a Schiff base, which can be stabilized by NaBH4 treatment. Several types of DNA containing the AP site were used to trap proteins in human cell extracts by this method. In the case of single-stranded AP DNA and AP DNA duplex with both 5' and 3' dangling ends, the major crosslinking product had an apparent molecular mass of 45 kDa. Using peptide mass mapping based on mass spectrometry data, we identified the protein forming this adduct as an isoform of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) called "uracil-DNA glycosylase". GAPDH is a glycolytic enzyme with many additional putative functions, which include interaction with nucleic acids, different DNA damages and DNA repair enzymes. We investigated interaction of GAPDH purified from HeLa cells and rabbit muscles with different AP DNAs. In spite of the ability to form a Schiff-base intermediate with the deoxyribose of the AP site, GAPDH does not display the AP lyase activity. In addition, along with the borohydride-dependent adducts with AP DNAs containing single-stranded regions, GAPDH was also shown to form the stable borohydride-independent crosslinks with these AP DNAs. GAPDH was proven to crosslink preferentially to AP DNAs cleaved via the β-elimination mechanism (spontaneously or by AP lyases) as compared to DNAs containing the intact AP site. The level of GAPDH-AP DNA adduct formation depends on oxidation of the protein SH-groups; disulfide bond reduction in GAPDH leads to the loss of its ability to form the adducts with AP DNA. A possible role of formation of the stable adducts with AP sites by GAPDH is discussed.