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The Mixing Counterion Effect on DNA Compaction and Charge Neutralization at Low Ionic Strength
Yanwei Wang1, Ruxia Wang2, Tianyong Gao3
1College of Mathematical, Physics and Electronic Information Engineering, Wenzhou University, Wenzhou 325035, China. wangyw@wzu.edu.cn.
Polymers
|April 11, 2019
Summary
At low ionic strength, mixing counterions enhance DNA charge neutralization by multivalent cations, unlike at normal ionic strength. This promotes DNA compaction through cooperative electrostatic binding.
Area of Science:
- Biophysics
- Molecular Biology
- Electrochemistry
Background:
- DNA charge neutralization and compaction are crucial for biological processes.
- Multivalent counterions typically neutralize DNA charge, but this is affected by other ions.
- Previous studies showed suppression of charge neutralization with mixed ions at normal ionic strength.
Purpose of the Study:
- To investigate the effect of mixing counterions on DNA compaction and charge neutralization at low ionic strength.
- To understand the mechanism behind the observed effects of mixed counterions on DNA electrostatics.
Main Methods:
- Electrophoretic mobility measurements of DNA in solutions with mixed counterions.
- Single-molecule magnetic tweezers to measure DNA condensate forces.
- Varying concentrations of mono-, di-, and multivalent cations.
Main Results:
- Unlike at normal ionic strength, mixed mono- and di-valent cations promote DNA charge neutralization by multivalent cations at low ionic strength.
- Electrophoretic mobility of DNA increased in the presence of mixed counterions.
- DNA condensate forces confirmed enhanced compaction and neutralization.
Conclusions:
- The observed promotion of DNA charge neutralization by mixed counterions at low ionic strength is attributed to cooperative electrostatic binding.
- This effect is significant below a critical counterion concentration.
- Findings contrast with previous observations at normal ionic strength, highlighting the importance of ionic strength conditions.
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