Polγ coordinates DNA synthesis and proofreading to ensure mitochondrial genome integrity

  • Nat Struct Mol Biol. 2023 Jun;30(6):812-823. doi: 10.1038/s41594-023-00980-2.
Joon Park  1  2 ,  Geoffrey K Herrmann  1  2 ,  Patrick G Mitchell  3 ,  Michael B Sherman  1  2 ,  Y Whitney Yin  4  5  6
Affiliations
  • 1. Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA.
  • 2. Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, USA.
  • 3. Division of CryoEM and Bioimaging, Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center National Accelerator Laboratory, Stanford University, Menlo Park, CA, USA.
  • 4. Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA. [email protected].
  • 5. Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, USA. [email protected].
  • 6. Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA. [email protected].
PMID: 37202477 DOI: 10.1038/s41594-023-00980-2
Abstract

Accurate replication of mitochondrial DNA (mtDNA) by DNA Polymerase γ (Polγ) is essential for maintaining cellular energy supplies, metabolism, and cell cycle control. To illustrate the structural mechanism for Polγ coordinating polymerase (pol) and exonuclease (exo) activities to ensure rapid and accurate DNA synthesis, we determined four cryo-EM structures of Polγ captured after accurate or erroneous incorporation to a resolution of 2.4-3.0 Å. The structures show that Polγ employs a dual-checkpoint mechanism to sense nucleotide misincorporation and initiate proofreading. The transition from replication to error editing is accompanied by increased dynamics in both DNA and enzyme, in which the polymerase relaxes its processivity and the primer-template DNA unwinds, rotates, and backtracks to shuttle the mismatch-containing primer terminus 32 Å to the exo site for editing. Our structural and functional studies also provide a foundation for analyses of Polγ mutation-induced human diseases and aging.