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Single-Molecule Real-Time Visualization of DNA Unwinding by CMG Helicase
Published on: September 27, 2024
Structural basis for DNA duplex separation by a superfamily-2 helicase
Katharina Büttner1, Sebastian Nehring, Karl-Peter Hopfner
1Center for Integrated Protein Science, Gene Center and Department of Chemistry and Biochemistry, Ludwig-Maximilians-University Munich, Feodor-Lynen-Str. 25, 81377 Munich, Germany.
Nature Structural & Molecular Biology
|June 15, 2007
Summary
This study reveals how Superfamily-2 (SF2) 3'-->5' helicases unwind DNA. A key beta-hairpin loop facilitates initial strand separation, with ATP enabling processive unwinding.
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- Superfamily-2 (SF2) helicases are crucial enzymes involved in DNA metabolism.
- Understanding their mechanism, particularly processive strand separation, is essential for comprehending DNA replication and repair.
- Archaeal Hel308, related to human DNA polymerase theta, serves as a model for studying 3'-->5' SF2 helicases.
Purpose of the Study:
- To elucidate the mechanism of processive strand separation by SF2 3'-->5' helicases.
- To determine the structural basis of DNA unwinding by archaeal Hel308.
- To compare the mechanism of SF2 helicases with SF1 helicases.
Main Methods:
- Determined apo and DNA-bound crystal structures of archaeal Hel308.
- Captured the duplex-unwinding reaction in a structural context.
- Compared structures of ATP-free and ATP-bound SF2 enzymes.
Main Results:
- Identified a prominent beta-hairpin loop as the key unwinding element.
- Demonstrated that initial strand separation does not require ATP.
- Showed that ATP promotes processive unwinding via ratchet-like transport of the 3' product strand.
- Found similar unwinding elements in other SF2 helicases, suggesting a conserved mechanism.
Conclusions:
- Provided the first structural framework for strand separation by processive SF2 3'-->5' helicases.
- Revealed mechanistic differences between SF2 and SF1 helicases.
- The identified beta-hairpin loop mechanism is likely applicable to a broad range of SF2 helicases.
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