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Mechanisms of a ring shaped helicase
1Department of Biochemistry, UMDNJ, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
Nucleic Acids Research
|August 29, 2006
Summary
Bacteriophage T7 helicase, a ring-shaped enzyme, efficiently translocates along DNA. Its unwinding activity is slow but significantly enhanced when coupled with DNA synthesis by T7 DNA polymerase.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Bacteriophage T7 helicase (gene 4 helicase-primase) is a well-studied, ring-shaped hexameric helicase.
- It binds single-stranded DNA within its central channel.
- Its structure and biochemical mechanisms are extensively characterized.
Purpose of the Study:
- To detail the biochemical mechanisms of T7 helicase action.
- To highlight key findings regarding its DNA binding, translocation, and unwinding activities.
- To discuss potential mechanisms of helicase function using T7 helicase as a model.
Main Methods:
- Biochemical assays to study nucleotide hydrolysis and DNA binding.
- DNA unwinding assays.
- Coupling assays with T7 DNA polymerase.
Main Results:
- T7 helicase forms a homohexameric ring utilizing RecA-type motifs for NTP binding and hydrolysis.
- Deoxythymidine triphosphate (dTTP) optimizes T7 helicase assembly, DNA binding, and unwinding.
- Subunit-specific dTTP hydrolysis occurs during translocation and likely during unwinding.
- Unwinding is significantly slower than translocation but is stimulated by coupled DNA synthesis.
Conclusions:
- T7 helicase exhibits distinct translocation and unwinding rates.
- Coupling DNA synthesis to unwinding enhances T7 helicase efficiency.
- The study provides insights into helicase mechanisms using T7 helicase as a model system.
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