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Analyzing and Building Nucleic Acid Structures with 3DNA
Published on: April 26, 2013
DNA structural deformations in the interaction of the controller protein C.AhdI with its operator sequence
I Papapanagiotou1, S D Streeter, P D Cary
1Biophysics Laboratories, Institute of Biomedical and Biomolecular Science, St Michael's Building, University of Portsmouth, PO1 2DT, UK.
Nucleic Acids Research
|April 12, 2007
Summary
Controller protein C.AhdI binds bacterial DNA operator sequences to regulate gene expression. Studies reveal C.AhdI binding causes significant DNA distortion, with distinct structural changes observed in dimeric and tetrameric complexes.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- Controller proteins like C.AhdI are crucial for regulating bacterial restriction-modification systems.
- These proteins ensure DNA methylation precedes endonuclease activity by delaying gene transcription.
- C.AhdI binds to a specific operator DNA sequence comprising O(L) and O(R) sites.
Purpose of the Study:
- To investigate the binding of C.AhdI to its operator DNA sequences.
- To characterize the structural changes induced in DNA upon C.AhdI binding using biophysical techniques.
- To elucidate the formation and structural features of dimeric and tetrameric C.AhdI-DNA complexes.
Main Methods:
- Circular permutation DNA-bending assays were employed to measure DNA bending angles.
- Circular dichroism (CD) spectroscopy was used to assess DNA structural distortions.
- Analysis of binding to single (O(L)) and double (O(L) + O(R)) sites was performed.
Main Results:
- CD spectroscopy revealed significant DNA distortion upon C.AhdI binding.
- Binding to one or two sites (dimeric and tetrameric complexes) increased the CD signal at 278 nm by 40% and 80%, respectively.
- DNA bending assays showed comparable bend angles for dimeric (47°) and tetrameric (38°) complexes, indicating localized distortion.
Conclusions:
- C.AhdI binding induces substantial local DNA distortion at both O(L) and O(R) sites.
- The relative orientation of dimers within the tetrameric complex and the role of conserved Py-A-T sequences are key structural considerations.
- These findings contribute to understanding the mechanism of gene regulation by C.AhdI in bacterial systems.
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