Biology:T7 DNA helicase
| DNA primase/helicase | |||||||
|---|---|---|---|---|---|---|---|
| Identifiers | |||||||
| Organism | |||||||
| Symbol | 4 | ||||||
| UniProt | P03692 | ||||||
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T7 DNA helicase (gp4) is a hexameric motor protein encoded by T7 phages that uses energy from dTTP hydrolysis to process unidirectionally along single stranded DNA, separating (helicase) the two strands as it progresses. It is also a primase, making short stretches of RNA that initiates DNA synthesis.[1] It forms a complex with T7 DNA polymerase. Its homologs are found in mitochondria (as Twinkle) and chloroplasts.[2][3]
Crystal structure
The crystal structure was solved to 3.0 Å resolution in 2000, as shown in the figure in the reference.[4] In (A), notice that the separate subunits appear to be anchored through interactions between an alpha helix and an adjacent subunit. In (B), there are six sets of three loops. The red loop, known as loop II, contains three lysine residues and is thought to be involved in binding the ssDNA that is fed through the center of the enzyme.
Mechanism of sequential dTTP hydrolysis
Crampton et al. have proposed a mechanism for the ssDNA-dependent hydrolysis of dTTP by T7 DNA helicase as shown in the figure below.[5] In their model, protein loops located on each hexameric subunit, each of which contain three lysine residues, sequentially interact with the negatively charged phosphate backbone of ssDNA. This interaction presumably causes a conformational change in the actively bound subunit, providing for the efficient release of dTDP from its dTTP binding site. In the process of dTDP release, the ssDNA is transferred to the neighboring subunit, which undergoes a similar process. Previous studies have already suggested that ssDNA is able to bind to two hexameric subunits simultaneously.[6]
See also
References
- ↑ "Choreography of bacteriophage T7 DNA replication". Current Opinion in Chemical Biology 15 (5): 580–586. October 2011. doi:10.1016/j.cbpa.2011.07.024. PMID 21907611.
- ↑ "Human mitochondrial DNA deletions associated with mutations in the gene encoding Twinkle, a phage T7 gene 4-like protein localized in mitochondria". Nature Genetics 28 (3): 223–231. July 2001. doi:10.1038/90058. PMID 11431692.
- ↑ "The Arabidopsis At1g30680 gene encodes a homologue to the phage T7 gp4 protein that has both DNA primase and DNA helicase activities". BMC Plant Biology 13: 36. March 2013. doi:10.1186/1471-2229-13-36. PMID 23452619.
- ↑ "Crystal structure of T7 gene 4 ring helicase indicates a mechanism for sequential hydrolysis of nucleotides". Cell 101 (6): 589–600. June 2000. doi:10.1016/S0092-8674(00)80871-5. PMID 10892646.
- ↑ "DNA-induced switch from independent to sequential dTTP hydrolysis in the bacteriophage T7 DNA helicase". Molecular Cell 21 (2): 165–174. January 2006. doi:10.1016/j.molcel.2005.11.027. PMID 16427007.
- ↑ "DNA is bound within the central hole to one or two of the six subunits of the T7 DNA helicase". Nature Structural Biology 3 (9): 740–743. September 1996. doi:10.1038/nsb0996-740. PMID 8784344.
External links
- T7+DNA+Primase-Helicase+Protein at the US National Library of Medicine Medical Subject Headings (MeSH)
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