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'''Integrase''' is an enzyme produced by a [[retrovirus]] (such as [[HIV]]) that enables its genetic material to be [[retroviral integration|integrated]] into the DNA of the infected cell. It is also produced by viruses containing double-stranded DNAs for the same purpose.
'''Retroviral integrase''' (IN) is an enzyme produced by a [[retrovirus]] (such as [[HIV]]) that enables its genetic material to be [[retroviral integration|integrated]] into the DNA of the infected cell. Retroviral INs are not to be confused with phage integrases, such as λ phage integrase (Int) (see [[site-specific recombination]]).


It is a key component in the [[pre-integration complex]] (PIC).
IN is a key component in the retroviral [[pre-integration complex]] (PIC).


==Structure==
==Structure==
All retroviral IN proteins contain three canonical domains, connected by flexible linkers:
The integrase protein contains three domains:
* an [[N-terminal]] HH-CC [[zinc finger]] [[protein domain|domain]] believed to be partially responsible for multimerization
* an [[N-terminal]] HH-CC zinc-binding domain (a three-helical bundle stabilised by coordination of a Zn(II) cation)
* a central catalytic domain
* a catalytic core domain (RNaseH fold)
* a [[C-terminal]].
* a [[C-terminal]] domain ([[SH3 domain|SH3 fold]])


Both the Central catalytic domain and C-terminal domains have been shown to bind both viral and cellular DNA. Early in 2010, scientists announced that they had grown a crystal allowing detailed analysis of the structure of integrase.<ref>http://www.reuters.com/article/idUSLDE60T0F820100131?type=marketsNews</ref>
Biochemical data and structural data suggest that retroviral IN functions as a [[Tetrameric protein|tetramer]] (dimer-of-dimers). All three domains are important for multimerisation and viral DNA binding. Early in 2010, scientists announced that they had grown a crystal allowing detailed analysis of the structure of IN from prototype foamy virus (PFV) assembled on viral DNA ends.<ref>http://www.reuters.com/article/idUSLDE60T0F820100131?type=marketsNews</ref>


In addition, several host cellular proteins have been shown to interact with IN to facilitate the integration process. Human chromatin-associated protein LEDGF, which tightly binds HIV IN and directs HIV PIC towards highly-expressed genes for integration, is an example of such a host factor.
Biochemical data and structural data suggest that integrase functions as a [[dimer]] or a [[Tetrameric protein|tetramer]].

In addition, several host cellular proteins have been shown to interact with integrase and may facilitate the integration process.


==Function==
==Function==
Integration occurs following production of the double-stranded viral DNA by the viral DNA polymerase, [[reverse transcriptase]].
Integration occurs following production of the double-stranded viral DNA by the viral RNA/DNA-dependent DNA polymerase, [[reverse transcriptase]].


The main function of IN is to insert the viral DNA into the host chromosomal DNA, a step that is essential for [[HIV]] replication. Integration is a point of no return for the cell, which becomes a permanent carrier of the viral genome (provirus). Integration is in part responsible for the persistence of retroviral infections. After integration, the viral gene expression and particle production may take place immediately or at some point in the future. The timing presumably depends on the activity of the chromosomal locus hosting the provirus.
Integrase acts to insert the proviral DNA into the host chromosomal DNA, a step that is essential for [[HIV]] replication.


Integrase catalyzes two reactions:
Retroviral IN catalyzes two reactions:
* 3'-end processing, in which two [[deoxynucleotides]] are removed from the 3' ends of the viral DNA.
* 3'-processing, in which two or three nucleotides are removed from one or both 3' ends of the viral DNA to expose the invariant CA dinucleotides at both 3'-ends of the viral DNA.
* the strand transfer reaction, in which the processed 3' ends of the viral DNA are covalently ligated to the host chromosomal DNA.
* the strand transfer reaction, in which the processed 3' ends of the viral DNA are covalently ligated to the host chromosomal DNA.


Importantly, both reactions are catalysed by the same active site and occur via [[transesterification]], without a [[covalent]] protein-DNA intermediate, in contrast to reactions catalysed by Ser and Tyr recombinases (see [[site specific recombination]]).
Integration of the proviral DNA is essential for the subsequent transcription of the viral genome, which leads to production of new viral genomic [[RNA]] and viral proteins needed for the production of the next round of infectious virus.

In essence, the process involving integrase is a key step in allowing viral DNA to become a permanent member of the host genome. This integrated proviral DNA is then translated using host cell machinery (see [[Translation (biology)|translation]]) into viral proteins.


==HIV integrase==
==HIV IN==
'''[[HIV]] integrase''' is a 32 [[kilodalton|kDa]] [[protein]] produced from the C-terminal portion of the Pol gene product, and is an attractive target for new anti-HIV drugs.
'''[[HIV]] integrase''' is a 32 [[kilodalton|kDa]] [[protein]] produced from the C-terminal portion of the Pol gene product, and is an attractive target for new anti-HIV drugs.


Revision as of 11:12, 26 April 2010

Retroviral integrase (IN) is an enzyme produced by a retrovirus (such as HIV) that enables its genetic material to be integrated into the DNA of the infected cell. Retroviral INs are not to be confused with phage integrases, such as λ phage integrase (Int) (see site-specific recombination).

IN is a key component in the retroviral pre-integration complex (PIC).

Structure

All retroviral IN proteins contain three canonical domains, connected by flexible linkers:

  • an N-terminal HH-CC zinc-binding domain (a three-helical bundle stabilised by coordination of a Zn(II) cation)
  • a catalytic core domain (RNaseH fold)
  • a C-terminal domain (SH3 fold)

Biochemical data and structural data suggest that retroviral IN functions as a tetramer (dimer-of-dimers). All three domains are important for multimerisation and viral DNA binding. Early in 2010, scientists announced that they had grown a crystal allowing detailed analysis of the structure of IN from prototype foamy virus (PFV) assembled on viral DNA ends.[1]

In addition, several host cellular proteins have been shown to interact with IN to facilitate the integration process. Human chromatin-associated protein LEDGF, which tightly binds HIV IN and directs HIV PIC towards highly-expressed genes for integration, is an example of such a host factor.

Function

Integration occurs following production of the double-stranded viral DNA by the viral RNA/DNA-dependent DNA polymerase, reverse transcriptase.

The main function of IN is to insert the viral DNA into the host chromosomal DNA, a step that is essential for HIV replication. Integration is a point of no return for the cell, which becomes a permanent carrier of the viral genome (provirus). Integration is in part responsible for the persistence of retroviral infections. After integration, the viral gene expression and particle production may take place immediately or at some point in the future. The timing presumably depends on the activity of the chromosomal locus hosting the provirus.

Retroviral IN catalyzes two reactions:

  • 3'-processing, in which two or three nucleotides are removed from one or both 3' ends of the viral DNA to expose the invariant CA dinucleotides at both 3'-ends of the viral DNA.
  • the strand transfer reaction, in which the processed 3' ends of the viral DNA are covalently ligated to the host chromosomal DNA.

Importantly, both reactions are catalysed by the same active site and occur via transesterification, without a covalent protein-DNA intermediate, in contrast to reactions catalysed by Ser and Tyr recombinases (see site specific recombination).

HIV IN

HIV integrase is a 32 kDa protein produced from the C-terminal portion of the Pol gene product, and is an attractive target for new anti-HIV drugs.

In November 2005, data from a phase 2 study of an investigational HIV integrase inhibitor, MK-0518, demonstrated that the compound had potent antiviral activity. [2][3]On October 12, 2007, the Food and Drug Administration (U.S.) approved the integrase inhibitor Raltegravir (MK-0518, brand name Isentress TM). [4] As of April 2008, this is the only integrase inhibitor approved for treating HIV Infection.

On February 1, 2010, it was reported that researchers at Imperial College London had solved a crucial puzzle about the AIDS virus after 20 years of research and that their findings could lead to better treatments for HIV.[5] This was accomplished by growing a crystal that revealed the structure of human foamy virus integrase. Elucidation of the HIV-1 integrase structure has been unsuccessful despite numerous efforts.

References

  1. ^ http://www.reuters.com/article/idUSLDE60T0F820100131?type=marketsNews
  2. ^ Morales-Ramirez JO, Teppler H, Kovacs C, et al. Antiretroviral effect of MK-0518, a novel HIV-1 integrase inhibitor, in ART-naïve HIV-1 infected patients. Program and abstracts of the 10th European AIDS Conference; November 17-20, 2005; Dublin, Ireland. Abstract LBPS1/6. Online summary: http://clinicaloptions.com/HIV/Conference%20Coverage/Dublin%202005/Capsules/LBPS1-6.aspx
  3. ^ Savarino A (2006). "A historical sketch of the discovery and development of HIV-1 integrase inhibitors". Expert Opin Investig Drugs. 15 (12): 1507–22. doi:10.1517/13543784.15.12.1507. PMID 17107277. {{cite journal}}: Unknown parameter |month= ignored (help)
  4. ^ FDA approves drug that fights HIV in new way - CNN.com
  5. ^ Hare S; Gupta SS; Valkov E; Engelman A; Cherepanov P (2010) Retroviral intasome assembly and inhibition of DNA strand transfer. Nature. (in press)
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