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Preparation of Nucleosome Core Particles Complexed with DNA Repair Factors for Cryo-Electron Microscopy Structural Determination
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Structural basis for APE1 processing DNA damage in the nucleosome.

Tyler M Weaver1,2, Nicole M Hoitsma1, Jonah J Spencer1

  • 1Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, USA.

Nature Communications
|September 14, 2022
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Summary
This summary is machine-generated.

DNA repair enzyme AP-endonuclease 1 (APE1) efficiently repairs DNA damage within nucleosomes by sculpting DNA. This mechanism overcomes the barrier posed by nucleosomes, ensuring genomic stability and effective base excision repair.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Genomic DNA faces constant damage from internal and external sources.
  • Nucleosomes, DNA packaging structures, impede DNA repair processes.
  • Mechanisms for DNA repair proteins to access and repair nucleosomal DNA are largely unknown.

Purpose of the Study:

  • To elucidate how AP-endonuclease 1 (APE1) recognizes and cleaves DNA damage within nucleosomes.
  • To understand how DNA repair proteins overcome nucleosomal barriers to maintain genomic stability.

Main Methods:

  • Kinetic assays to measure APE1 cleavage efficiency.
  • Cryo-electron microscopy to determine structural mechanisms.
  • Biochemical and structural characterization of nucleosome-DNA interactions.

Main Results:

  • APE1 shows significantly higher efficiency (3-6 orders of magnitude) in cleaving solvent-exposed versus occluded AP sites in nucleosomes.
  • Cryo-EM reveals APE1 employs a DNA sculpting mechanism, bending nucleosomal DNA to access AP sites.
  • Occluded AP sites are hindered by DNA-histone octamer contacts, preventing efficient APE1 processing.

Conclusions:

  • APE1's DNA sculpting ability is crucial for recognizing and processing AP sites in nucleosomes.
  • The position-dependent activity of BER proteins is explained by their interaction with nucleosomal DNA.
  • DNA sculpting by BER proteins is essential for efficient base excision repair in chromatin.