Superior removal of hydantoin lesions relative to other oxidized bases by the human DNA glycosylase hNEIL1.
The DNA glycosylase hNEIL1 initiates the base excision repair (BER) of a diverse array of lesions, including ring-opened purines and saturated pyrimidines. Of these, the hydantoin lesions, guanidinohydantoin (Gh) and the two diastereomers of spiroiminodihydantoin (Sp1 and Sp2), have garnered much recent attention due to their unusual structures, high mutagenic potential, and detection in cells. In order to provide insight into the role of repair, the excision efficiency by hNEIL1 of these hydantoin lesions relative to other known substrates was determined. Most notably, quantitative examination of the substrate specificity with hNEIL1 revealed that the hydantoin lesions are excised much more efficiently (>100-fold faster) than the reported standard substrates thymine glycol (Tg) and 5-hydroxycytosine (5-OHC). Importantly, the glycosylase and beta,delta-lyase reactions are tightly coupled such that the rate of the lyase activity does not influence the observed substrate specificity. The activity of hNEIL1 is also influenced by the base pair partner of the lesion, with both Gh and Sp removal being more efficient when paired with T, G, or C than when paired with A. Notably, the most efficient removal is observed with the Gh or Sp paired in the unlikely physiological context with T; indeed, this may be a consequence of the unstable nature of base pairs with T. However, the facile removal via BER in promutagenic base pairs that are reasonably formed after replication (such as Gh.G) may be a factor that modulates the mutagenic profile of these lesions. In addition, hNEIL1 excises Sp1 faster than Sp2, indicating the enzyme can discriminate between the two diastereomers. This is the first time that a BER glycosylase has been shown to be able to preferentially excise one diastereomer of Sp. This may be a consequence of the architecture of the active site of hNEIL1 and the structural uniqueness of the Sp lesion. These results indicate that the hydantoin lesions are the best substrates identified thus far for hNEIL1 and suggest that repair of these lesions may be a critical function of the hNEIL1 enzyme in vivo.
Krishnamurthy
Nirmala
N
Department of Chemistry, University of Utah, 315 South, 1400 East, Salt Lake City, Utah 84112, USA.
Zhao
Xiaobei
X
Burrows
Cynthia J
CJ
David
Sheila S
SS
D001483:Base Sequence; D001665:Binding Sites; D003198:Computer Simulation; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004249:DNA Damage; D045647:DNA Glycosylases / Q000378:metabolism*; D004260:DNA Repair; D004795:Enzyme Stability; D006146:Guanidines / Q000737:chemistry / Q000378:metabolism*; D006151:Guanosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006827:Hydantoins / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D011687:Purines / Q000737:chemistry / Q000378:metabolism*; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism*; D013141:Spiro Compounds / Q000737:chemistry / Q000378:metabolism*; D013237:Stereoisomerism
D006146:Guanidines; D006827:Hydantoins; D011687:Purines; D011743:Pyrimidines; D013141:Spiro Compounds; C467338:guanidinohydantoin; C408822:spiroiminodihydantoin; D006151:Guanosine; D004247:DNA; D045647:DNA Glycosylases; C473634:NEIL1 protein, human