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Complexes of RecA protein in solution. A study by small angle neutron scattering
E DiCapua1, M Schnarr, R W Ruigrok
1Institut Laue-Langevin, Grenoble, France.
Journal of Molecular Biology
|July 20, 1990
Summary
RecA protein filaments exist in two distinct structural states: an active, open helical form when bound to DNA with ATP, and a compact, inactive form under other conditions. These findings reconcile conflicting structural data.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biophysics
Background:
- RecA protein is crucial for DNA repair and recombination.
- Previous structural studies of RecA complexes have yielded conflicting results.
- Understanding RecA filament structure is key to elucidating its biological functions.
Purpose of the Study:
- To resolve conflicting structural data on RecA filaments.
- To characterize the distinct structural states of RecA complexes in solution.
- To correlate RecA filament structure with enzyme activity.
Main Methods:
- Small-angle neutron scattering (SANS) was employed to analyze RecA complexes.
- Guinier analysis was used for small-angle scattering data.
- Model analysis of subsidiary peaks provided detailed structural insights.
Main Results:
- Two RecA filament structures were identified: an active, open helix (95 Å pitch) and an inactive, compact helix (70 Å pitch).
- The active state involves RecA bound to DNA with ATPγS, exhibiting specific dimensions and mass per length.
- The inactive state includes RecA bound to ssDNA without ATP, or RecA with ATPγS without DNA, or RecA alone.
Conclusions:
- The study successfully reconciles conflicting electron microscopy data by defining two distinct RecA filament structures.
- The identified structures correlate with the active (DNA/ATP) and inactive (various conditions) states of the enzyme.
- These findings provide a unified structural model for RecA filament function.