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Structural basis for the functional switch of the E. coli Ada protein
1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
Biochemistry
|April 4, 2001
Summary
The Escherichia coli Ada protein repairs DNA methyl phosphotriesters by transferring a methyl group to itself. This methylation converts Ada into a transcriptional activator, enhancing DNA repair mechanisms.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- DNA methyl phosphotriesters are DNA adducts that require specific repair mechanisms.
- The Escherichia coli Ada protein acts as a chemosensor, repairing DNA damage and activating repair genes.
- Understanding the structural basis of Ada's function is crucial for deciphering DNA repair and transcriptional regulation.
Purpose of the Study:
- To determine the refined solution structure of the N-terminal domain of Ada (N-Ada10).
- To elucidate the structural mechanism underlying the conformational switch in Ada upon methyl transfer.
- To investigate the role of the zinc-thiolate center and methyl group in Ada's transcriptional activation.
Main Methods:
- High-resolution solution structure determination of N-Ada10.
- Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near-Edge Structure (XANES) spectroscopy.
- Nuclear Overhauser Effect SpectroscopY (NOESY) with specifically labeled methylated-Ada/DNA complexes.
Main Results:
- A refined solution structure of N-Ada10 revealing details of its nonspecific DNA interaction.
- Confirmation that the zinc-thiolate center is maintained after methylation, ruling out ligand exchange as the activation mechanism.
- NOESY data indicating the transferred methyl group contacts within N-Ada, not the DNA, suggesting an allosteric conformational change.
Conclusions:
- Methylation of Ada induces a structural change, remodeling its surface for enhanced promoter binding.
- The conformational switch is an allosteric process, not directly involving the transferred methyl group's interaction with DNA.
- Ada's mechanism provides a model for chemosensing and adaptive repair in response to DNA damage.
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