Related Experiment Videos
Electrostatic contributions to site specific DNA cleavage by EcoRV endonuclease
Nancy C Horton1, Christopher Otey, Shelley Lusetti
1Department of Chemistry and Biochemistry and Interdepartmental Program in Biomolecular Science and Engineering, University of California at Santa Barbara, Santa Barbara, California 93106-9510, USA.
Biochemistry
|August 28, 2002
Summary
Electrostatic interactions near the EcoRV endonuclease active site significantly influence DNA cleavage efficiency. Modifying charged amino acids alters catalysis, revealing insights into enzyme-DNA binding and conformational changes.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- The EcoRV endonuclease is a key enzyme involved in DNA processing.
- Understanding the catalytic mechanisms of restriction enzymes like EcoRV is crucial for molecular biology applications.
- Electrostatic interactions are known to play roles in enzyme function, but their specific contributions in EcoRV require further elucidation.
Purpose of the Study:
- To investigate the role of peripheral amino acids and electrostatic effects in modulating EcoRV endonuclease activity.
- To determine how mutations affecting charge distribution impact the catalytic efficiency of phosphoryl transfer.
- To elucidate the contribution of Glu45 to DNA binding-induced conformational changes and active site assembly.
Main Methods:
- Site-directed mutagenesis was employed to alter specific amino acid residues (Asp36, Lys38, Lys173, Glu45) in the EcoRV endonuclease.
- Kinetic analyses were performed to measure the catalytic rates of wild-type and mutant enzymes.
- Crystallographic studies, including X-ray diffraction, were used to determine the structures of mutant enzymes bound to DNA and metal ions (Mn2+).
Main Results:
- Mutations at Asp36 and Lys38 significantly decreased catalytic rates (10^3-10^5-fold), while charge-rebalancing double mutants showed improved catalysis (up to 500-fold).
- Lys173's proximity to the active site suggests its involvement in modulating catalytic efficiency.
- The E45A mutation induced significant conformational changes in the dimer interface and major-groove binding loops, altering the enzyme's electrostatic potential and disrupting Mn2+ binding, without directly affecting active site structure.
Conclusions:
- Moderate-range electrostatic effects, particularly from peripheral residues, are critical for efficient phosphoryl transfer in EcoRV.
- The Glu45 residue plays a significant role in facilitating DNA-induced conformational transitions essential for active site assembly and metal ion coordination.
- These findings challenge the proposed role of Asp36 as a general base and highlight the importance of electrostatic potential in enzyme-DNA recognition and catalysis.