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Positively charged surfaces increase the flexibility of DNA
Alessandro Podestà1, Marco Indrieri, Doriano Brogioli
1Department of Physics, INFM and CIMAINA, and Department of Biology and CIMAINA, University of Milan, Milan, Italy.
Biophysical Journal
|July 26, 2005
Summary
Researchers found that DNA flexibility significantly increases on charged surfaces, up to fivefold. This suggests that proteins may alter DNA stiffness by modulating phosphate repulsions, impacting processes like chromatin stability.
Area of Science:
- Biophysics
- Molecular Biology
- Materials Science
Background:
- Proteins bind DNA via positive amino acids, but may also alter DNA stiffness.
- DNA flexibility in solution is well-studied, but less is known on charged surfaces like nucleosomes.
- Understanding DNA flexibility on surfaces is crucial for processes like chromatin packaging.
Purpose of the Study:
- To investigate how charged surfaces affect DNA flexibility.
- To quantify the change in DNA stiffness due to charge modulation.
- To develop a method for measuring DNA flexibility on charged substrates.
Main Methods:
- Utilized scanning force microscopy to measure DNA flexibility.
- Employed mica coated with varying concentrations and types of polyamines as a substrate.
- Applied theoretical models relating charge neutralization to DNA flexibility.
Main Results:
- DNA flexibility increased up to fivefold on polyamine-coated mica.
- Predicted approximately 50% attenuation of phosphate repulsions in the most flexible DNA.
- Demonstrated a simple method for assessing DNA flexibility on charged surfaces.
Conclusions:
- Charged surfaces, mimicking biological environments, significantly enhance DNA flexibility.
- Modulation of DNA phosphate repulsions by charged surfaces is a key factor in DNA bending and packaging.
- This method provides insights into DNA mechanics relevant to chromatin stability and viral encapsulation.