Integrase
Encyclopedia
Retroviral integrase 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).
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.
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.
.
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, it is presumed, depends on the activity of the chromosomal locus hosting the provirus.
Retroviral IN catalyzes two reactions:
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).
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 has potent antiviral activity. On October 12, 2007, the Food and Drug Administration (U.S.) approved the integrase inhibitor Raltegravir (MK-0518, brand name Isentress TM). 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. 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.
Retrovirus
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
(such as HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
) 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
Site-specific recombination
Site-specific recombination, also known as conservative site-specific recombination, is a type of genetic recombination in which DNA strand exchange takes place between segments possessing only a limited degree of sequence homology...
).
IN is a key component in the retroviral pre-integration complex
Pre-integration complex
The pre-integration complex is a nucleoprotein complex of viral genetic material and associated viral and host proteins. The PIC forms after uncoating of a viral particle after entry into the host cell...
(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 DNA-binding domain (SH3 foldSH3 domainThe SRC Homology 3 Domain is a small protein domain of about 60 amino acids residues first identified as a conserved sequence in the viral adaptor protein v-Crk and the non-catalytic parts of enzymes such as phospholipase and several cytoplasmic tyrosine kinases such as Abl and Src...
)
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.
In addition, several host cellular proteins have been shown to interact with IN to facilitate the integration process. Human chromatin-associated protein LEDGF
PSIP1
PC4 and SFRS1 interacting protein 1, also known as lens epithelium-derived growth factor , dense fine speckles 70kD protein or transcriptional coactivator p75/p52, is a protein which in humans is encoded by the PSIP1 gene.- Function :...
, 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 transcriptaseReverse transcriptase
In the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...
.
The main function of IN is to insert the viral DNA into the host chromosomal DNA, a step that is essential for HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
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, it is presumed, 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.
Both reactions are catalysed by the same active site and occur via transesterification
Transesterification
In organic chemistry, transesterification is the process of exchanging the organic group R″ of an ester with the organic group R′ of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst...
, without a covalent protein-DNA intermediate, in contrast to reactions catalysed by Ser and Tyr recombinases (see site specific recombination).
HIV IN
HIVHIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
integrase is a 32 kDa protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
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
Clinical trial
Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...
of an investigational HIV integrase inhibitor
Integrase inhibitor
Integrase inhibitors are a class of antiretroviral drug designed to block the action of integrase, a viral enzyme that inserts the viral genome into the DNA of the host cell. Since integration is a vital step in retroviral replication, blocking it can halt further spread of the virus...
, MK-0518
MK-0518
Raltegravir is an antiretroviral drug produced by Merck & Co., used to treat HIV infection. It received approval by the U.S...
, demonstrated that the compound has potent antiviral activity. On October 12, 2007, the Food and Drug Administration (U.S.) approved the integrase inhibitor Raltegravir (MK-0518, brand name Isentress TM). 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
Imperial College London
Imperial College London is a public research university located in London, United Kingdom, specialising in science, engineering, business and medicine...
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. This was accomplished by growing a crystal that revealed the structure of human foamy virus
Human foamy virus
Human Foamy Virus is a retrovirus and specifically belongs to the genera Spumavirus. The spumaviruses are complex and significantly different from the other six genera or retroviruses in several ways...
integrase. Elucidation of the HIV-1 integrase structure has been unsuccessful despite numerous efforts.
External links
- http://discover.nci.nih.gov/pommier/IntegraseBookFull.pdf
- Specificity of Interaction of INI1/hSNF5 with Retroviral Integrases and Its Functional Significance
- Current status of gene therapy strategies to treat HIV/AIDS