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Direct observation of iron-induced conformational changes of mitochondrial DNA by high-resolution field-emission
Abstract:
When respiring rat liver mitochondria are incubated in the presence of Fe(III) gluconate, their DNA (mtDNA) relaxes from the supercoiled to the open circular form dependent on the iron dose. Anaerobiosis or antioxidants fail to completely inhibit the unwinding. High-resolution field-emission in-lens scanning electron microscopy imaging, in concert with backscattered electron detection, pinpoints nanometer-range iron colloids bound to mtDNA isolated from iron-exposed mitochondria. High-resolution field-emission in-lens scanning electron microscopy with backscattered electron detection imaging permits simultaneous detailed visual analysis of DNA topology, iron dose-dependent mtDNA unwinding, and assessment of iron colloid formation on mtDNA strands.
Insights
Iron exposure causes rat liver mitochondrial DNA (mtDNA) to unwind. Nanometer-range iron colloids bind to mtDNA, indicating a direct interaction between iron and DNA structure.
Area of Science:
- Mitochondrial biology
- Molecular toxicology
- Biophysics
Background:
- Mitochondrial DNA (mtDNA) integrity is crucial for cellular respiration and energy production.
- Iron overload is implicated in various pathologies, but its direct effect on mtDNA topology is not fully understood.
Purpose of the Study:
- To investigate the impact of Fe(III) gluconate on the structural integrity of rat liver mtDNA.
- To visualize and characterize the interaction between iron and mtDNA at the nanoscale.
Main Methods:
- Incubation of respiring rat liver mitochondria with varying doses of Fe(III) gluconate.
- High-resolution field-emission in-lens scanning electron microscopy (H-FIB-FESEM) with backscattered electron detection.
- Isolation and imaging of mtDNA from iron-exposed mitochondria.
Main Results:
- Fe(III) gluconate induces dose-dependent relaxation of supercoiled mtDNA to the open circular form.
- Anaerobiosis and antioxidants do not completely prevent mtDNA unwinding.
- H-FIB-FESEM reveals nanometer-range iron colloids directly bound to isolated mtDNA strands.
Conclusions:
- Iron exposure directly alters mtDNA topology, leading to unwinding and relaxation.
- Iron colloids form on mtDNA, suggesting a direct physical interaction mechanism.
- Advanced electron microscopy is effective for visualizing iron-DNA interactions and their structural consequences.