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DNA-binding induces a major structural transition in a type I methyltransferase
I A Taylor1, K G Davis, D Watts
1Biophysics Laboratories, University of Portsmouth, Portsmouth.
The EMBO Journal
|December 1, 1994
Summary
The DNA methyltransferase M.EcoR124I undergoes a significant structural change upon binding DNA, altering its shape to potentially access target bases. This transformation is independent of DNA methylation status.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biology
Background:
- Type IC DNA methyltransferases are complex enzymes.
- M.EcoR124I recognizes the specific DNA sequence GAAN6RTCG.
- Understanding enzyme-DNA interactions is crucial for molecular biology.
Purpose of the Study:
- To investigate the solution structure of M.EcoR124I.
- To determine how DNA binding affects the enzyme's quaternary structure.
- To explore the structural changes upon binding unmethylated and hemimethylated DNA.
Main Methods:
- Small angle X-ray scattering (SAXS) was used to study enzyme structure.
- Circular dichroism (CD) spectroscopy analyzed secondary structure changes.
- SAXS data provided radius of gyration and maximum dimension measurements.
Main Results:
- DNA binding induced a major quaternary structure change in M.EcoR124I.
- The radius of gyration decreased from 56 to 40 Å, and maximum dimension reduced from 180 to 112 Å.
- Structural transition was independent of DNA methylation state; DNA exhibited significant structural distortion.
Conclusions:
- DNA binding causes a substantial conformational change in M.EcoR124I.
- The enzyme's structural transition may facilitate access to DNA bases for methylation.
- A model involving HsdM subunit rotation mediated by HsdS hinge bending is proposed.