DNA polymerase λ inactivation by oxidized abasic sites

Area of Science:

• Molecular Biology
• Genomics
• Biochemistry

Background:

• Base excision repair (BER) is crucial for maintaining genomic integrity in mammalian cells.
• DNA polymerase lambda (Pol λ) is considered a backup polymerase in BER, complementing DNA polymerase beta (Pol β).
• Oxidized abasic lesions, such as pC4-AP and DOB, can be generated by DNA-damaging agents and pose a threat to genomic stability.

Purpose of the Study:

• To investigate the interactions between DNA polymerase lambda (Pol λ) and two specific oxidized abasic lesions: pC4-AP and DOB.
• To determine the efficiency of Pol λ in processing these lesions compared to Pol β.
• To elucidate the mechanism of inactivation of Pol λ by these lesions.

Main Methods:

• Single-turnover kinetic experiments were performed using DNA substrates containing DOB and pC4-AP lesions.
• Enzyme inactivation assays were conducted to quantify the inhibitory effects of DOB and pC4-AP on Pol λ.
• Mass spectral analysis was employed to identify the specific sites of modification on Pol λ upon inactivation.

Main Results:

• Pol λ exhibited significantly slower excision rates for DOB and pC4-AP compared to Pol β, indicating inefficient backup activity.
• DOB inactivated Pol λ less efficiently than Pol β due to a higher inhibition constant (K(I)).
• Both DOB and pC4-AP lesions were found to modify specific lysine residues (Lys324 and potentially Lys312) within the Pol λ active site, leading to inactivation of both lyase and polymerase activities.

Conclusions:

• DNA polymerase lambda (Pol λ) functions as an inefficient backup in base excision repair when dealing with oxidized abasic lesions.
• The inactivation of Pol λ by DOB and pC4-AP, involving modification of active site lysines, highlights the cytotoxic potential of these lesions.
• These findings underscore the importance of understanding lesion-BER polymerase interactions in the context of DNA damage and repair.