8‐oxo‐7,8‐dihydroxy‐2′‐deoxyguanosine (8‐oxo‐dG) has high mutagenic potential as it is prone to mispair with deoxyadenine (dA). In order to maintain genomic integrity, post‐replicative 8‐oxo‐dG:dA mispairs are removed through DNA polymerase lambda (Pol λ)‐dependent MUTYH‐initiated base excision repair (BER). Here, we describe seven novel crystal structures and kinetic data that fully characterize 8‐oxo‐dG bypass by Pol λ. We demonstrate that Pol λ has a flexible active site that can tolerate 8‐oxo‐dG in either the anti‐ or syn‐conformation. Importantly, we show that discrimination against the pro‐mutagenic syn‐conformation occurs at the extension step and identify the residue responsible for this selectivity. This residue acts as a kinetic switch, shunting repair toward long‐patch BER upon correct dCMP incorporation, thus enhancing repair efficiency. Moreover, this switch also provides a potential mechanism to increase repair fidelity of MUTYH‐initiated BER.
Structural analyses of DNA polymerase lambda (Pol λ) unveil its uniquely flexible active site accommodating 8‐oxo‐dGs irrespective of their conformation during bypass in base excision repair. At the extension step, discrimination is mediated by Glu529 and allows enhanced nucleotide selectivity and fidelity.
Pol λ tolerates 8‐oxo‐dG in either the anti‐ or syn‐conformation during nucleotide insertion.
Discrimination against the pro‐mutagenic syn‐conformation occurs during extension past the lesion.
This selectivity depends on a conserved active site residue in the thumb subdomain, Glu529.
Glu529 promotes extension past an 8‐oxo‐dG(anti):dC base pair and discourages extension past an 8‐oxo‐dG(syn):dA mispair.
Glu529 may shunt repair toward long‐path BER and increase repair fidelity.
- Received March 14, 2016.
- Revision received July 4, 2016.
- Accepted July 8, 2016.
- © 2016 The Authors
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