Related Experiment Video
Updated: May 30, 2026
Identification and Classification of Position-specific GABAA Receptor Subunit Missense Variants for Their Role In Hippocampal Pyramidal Neurons
Published on: June 6, 2025
Biochemical analysis of the G517V POLG variant reveals wild-type like activity
Rajesh Kasiviswanathan1, William C Copeland
1Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Abstract:
The c.1550g→t mutation in the POLG gene causing the G517V substitution has been reported by many groups to be associated with a variety of mitochondrial diseases, including autosomal dominant and recessive forms of ataxia neuropathy, myopathy and microcephaly, progressive external ophthalmoplegia, diabetes, strokes, hypotonia, and epilepsy. However, the variable disease presentation and age of onset raises suspicion of its pathogenicity. Because of the varied reported associated symptoms and request from physicians to address the consequence of this mutation, we have carried out the biochemical analysis of the purified recombinant human DNA polymerase γ protein harboring the G517V substitution. These analyses revealed that the G517V mutant enzyme retained 80-90% of wild-type DNA polymerase activity, in addition to its functional interaction with the p55 accessory subunit. DNA binding by the mutant was also only slightly lower than the wild-type enzyme. Our data suggest that the G517V mutation by itself in pol γ most likely does not have a role in mitochondrial disorders.
Insights
The G517V mutation in the POLG gene, linked to mitochondrial disorders, shows near-normal DNA polymerase activity and function. This suggests the G517V mutation alone may not cause these diseases.
Area of Science:
- Biochemistry
- Genetics
- Mitochondrial Biology
Background:
- The POLG gene encodes DNA polymerase gamma (pol γ), crucial for mitochondrial DNA replication.
- The c.1550g→t mutation leading to G517V substitution is frequently associated with diverse mitochondrial diseases.
- Variability in disease presentation and onset raises questions about the pathogenicity of the G517V mutation.
Purpose of the Study:
- To biochemically analyze the G517V substituted human DNA polymerase γ.
- To determine the functional impact of the G517V mutation on pol γ activity and interactions.
Main Methods:
- Purification of recombinant human DNA polymerase γ with the G517V substitution.
- Biochemical assays to measure DNA polymerase activity.
- Assessment of interaction with the p55 accessory subunit.
- Evaluation of DNA binding affinity.
Main Results:
- The G517V mutant pol γ retained 80-90% of wild-type enzyme activity.
- The mutant enzyme maintained functional interaction with the p55 accessory subunit.
- DNA binding by the G517V mutant was only slightly reduced compared to wild-type.
Conclusions:
- The G517V substitution in DNA polymerase γ exhibits robust enzymatic activity and normal subunit interaction.
- These findings indicate that the G517V mutation, in isolation, is unlikely to be pathogenic for mitochondrial disorders.
- Further research may be needed to identify co-factors or additional mutations contributing to disease phenotypes associated with POLG variants.
