DNA polymerase ? inactivation by oxidized abasic sites.

ABSTRACT: Base excision repair (BER) plays a vital role in maintaining genomic integrity in mammalian cells. DNA polymerase ? (Pol ?) is believed to play a backup role to DNA polymerase ? (Pol ?) in base excision repair. Two oxidized abasic lesions that are produced by a variety of DNA-damaging agents, including several antitumor antibiotics, the C4'-oxidized abasic site following Ape1 incision (pC4-AP), and 5'-(2-phosphoryl-1,4-dioxobutane) (DOB), irreversibly inactivate Pol ? and Pol ?. The interactions of DOB and pC4-AP with Pol ? are examined in detail using DNA substrates containing these lesions at defined sites. Single-turnover kinetic experiments show that Pol ? excises DOB almost 13 times more slowly than a 5'-phosphorylated 2-deoxyribose (dRP). pC4-AP is excised approximately twice as fast as DOB. The absolute rate constants are considerably slower than those reported for Pol ? for the respective reactions, suggesting that Pol ? may be an inefficient backup in BER. DOB inactivates Pol ? approximately 3-fold less efficiently than it does Pol ?, and the difference can be attributed to a higher K(I) (33 ± 7 nM). Inactivation of Pol ?'s lyase activity by DOB also prevents the enzyme from conducting polymerization following preincubation of the protein and DNA. Mass spectral analysis of GluC-digested Pol ? inactivated by DOB shows that Lys324 is modified. There is inferential support for the idea that Lys312 may also be modified. Both residues are within the Pol ? lyase active site. When acting on pC4-AP, Pol ? achieves approximately four turnovers on average before being inactivated. Lyase inactivation by pC4-AP is also accompanied by loss of polymerase activity, and mass spectrometry indicates that Lys312 and Lys324 are modified by the lesion. The ability of DOB and pC4-AP to inactivate Pol ? provides additional evidence that these lesions are significant sources of the cytotoxicity of DNA-damaging agents that produce them.

SUBMITTER: Stevens AJ 

PROVIDER: S-EPMC3566640 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature