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Structural flexibility in human topoisomerase I revealed in multiple non-isomorphous crystal structures
M R Redinbo1, L Stewart, J J Champoux
1Department of Biological Structure, School of Medicine, University of Washington, Seattle, WA 98195, USA.
Journal of Molecular Biology
|September 25, 1999
Summary
Human topoisomerase I (hTop1) is crucial for DNA stability. Structural analysis reveals significant conformational flexibility in hTop1, supporting its role in relaxing DNA superhelical tension.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biology
Background:
- Human topoisomerase I (hTop1) is essential for maintaining chromosomal stability.
- hTop1 resolves DNA superhelical tension during replication, transcription, and chromatin remodeling.
- The enzyme comprises N-terminal, core, linker, and C-terminal domains.
Purpose of the Study:
- To investigate the structural flexibility of human topoisomerase I.
- To elucidate the conformational changes related to DNA relaxation mechanisms.
- To analyze crystal structures of hTop1-DNA complexes.
Main Methods:
- X-ray crystallography of a truncated human topoisomerase I-DNA complex.
- Determination of eight crystal structures at 2.8-3.25 A resolution.
- Analysis of crystal packing and enzyme conformational flexibility.
Main Results:
- Observed significant crystal-to-crystal non-isomorphism and large shifts in cell constants.
- Identified dramatic shifts in crystal packing and functionally relevant conformational flexibility.
- The linker domain exhibited the greatest flexibility, with cap domain rotations and shifts also noted.
Conclusions:
- The observed conformational flexibility in the cap and linker domains supports the 'controlled rotation' mechanism for DNA superhelical tension relaxation.
- Structural plasticity of hTop1 is key to its enzymatic function in managing DNA topology.
- Understanding hTop1 flexibility provides insights into its role in nuclear processes and potential therapeutic targeting.