Multiprotein E. coli SSB-ssDNA complex shows both stable binding and rapid dissociation due to interprotein
M Nabuan Naufer1, Michael Morse1, Guðfríður Björg Möller1
1Department of Physics, Northeastern University, Boston, MA 02115, USA.
Nucleic Acids Research
|January 12, 2021
Summary
Escherichia coli SSB protein binds single-stranded DNA (ssDNA) in a biphasic manner, with high concentrations promoting unwrapping and dissociation for genome maintenance. This reveals dynamic ssDNA protection mechanisms.
Area of Science:
- Molecular Biology
- Biophysics
Background:
- Escherichia coli SSB (EcSSB) is a crucial protein for maintaining genome stability.
- It functions by binding to single-stranded DNA (ssDNA) and facilitates DNA replication and repair.
Purpose of the Study:
- To investigate the binding and wrapping dynamics of EcSSB on long ssDNA substrates under varying conditions.
- To elucidate the mechanism of ssDNA protection and protein dissociation.
Main Methods:
- Utilized single-molecule techniques to measure EcSSB binding and wrapping on ssDNA at fixed tensions.
- Manipulated substrate tension, length, and protein mutations to destabilize EcSSB wrapping.
Main Results:
- Observed biphasic binding kinetics with initial wrapping followed by unwrapping at higher protein densities.
- Identified an unstable, unwrapped bound state acting as a transition state for complex reorganization.
- Demonstrated stimulated dissociation of excess EcSSB at over-saturation, leaving stable complexes.
Conclusions:
- EcSSB exhibits dynamic binding and dissociation mechanisms crucial for ssDNA protection.
- These findings provide insights into how EcSSB facilitates DNA replication and repair by regulating its association with ssDNA.
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