Imperial College London


Faculty of MedicineDepartment of Infectious Disease

Reader in Molecular Virology



+44 (0)20 7594 3655g.maertens Website




314, Medical School BuildingNorfolk PlaceSt Mary's Campus





Interaction between Retroviral integrase and the host-cellular machinery.



Of the seven retroviral genera (lenti-, alpha-, beta-, gamma-, delta-, epsilon-, and spumavirinae), two are known to cause severe and fatal conditions in humans. The lentiviruses human immunodeficiency virus type 1 (HIV-1) and HIV-2 are the aetiological agents of acquired immunodeficiency syndrome. The deltaretrovirus HTLV-1 causes ATLL and the neurological disorder HAM/TSP. It is estimated that 10 to 20 million people worldwide are living with HTLV-1. Clonal expansion of infected cells and infectious spread to uninfected cells both contribute to viral persistence. Approximately 5% of HTLV-1-infected people eventually develop ATLL, of who most die within two years of presentation. The treatment of both the inflammatory and malignant diseases remains very unsatisfactory. Transmission, like HIV-1, occurs through sexual intercourse, blood transfusion, sharing of needles, organ transplantation and mother-to-child transmission either in utero or via breast milk. Strikingly, children who acquired HTLV-1 during childhood are much more likely to develop ATLL or HAM/TSP later in life.

To establish successful infection, a retrovirus must integrate a copy of its genome into a host cell chromosome. This reaction is catalyzed by the viral enzyme integrase (IN). A tetramer of IN binds and synapses viral DNA ends, forming a highly stable complex, referred to as intasome (Hare S. et al, 2010).  After transfer to the nucleus, IN joins the 3’ ends of viral DNA to host cell chromosomal DNA (Maertens G. et al, 2010; Hare S. et al, 2012 Serrao E. et al, 2014). A stable provirus is established after the repair of single-stranded gaps initially flanking the integrated viral DNA. This step is critical to establish infection. We have shown that IN strand transfer inhibitors (INSTIs) currently used in the clinic to treat HIV-1 seropositive patients efficiently block HTLV-1 integration in vitro and transmission in cell culture (Barski, M. S. et al, 2019Barski, M.S. et al, 2021; Schneiderman, B.S. et al, 2023). Thus the use of INSTIs as a (pre-exposure) prophylaxis is promising.

While the integration reaction ("cutting and pasting" of the viral cDNA copy into the host chromatin) is catalyzed by virally encoded IN, the targeting of the pre-integration complex (PIC) to the site of integration and the post-integration events to establish a stable provirus, are mediated by the interaction with host factors. Lentiviral INs (such as HIV-1) depend on the interaction with LEDGF/p75, which targets the PIC to actively transcribed chromatin (Reviewed in Engelman A. and Cherepanov P. 2008). We  (Gupta S.S. et al, 2013) and others have shown that gamma-retroviral PICs are targeted to promoter regions by the interaction with BET proteins. 

Genome-wide sequencing of HTLV-1 integration sites revealed a preference for integration in transcriptionally active regions of the genome, and a strong bias to integrate within close proximity of certain transcription factor binding sites (TFBS) (Melamed A. et al, 2013). I have identified an HTLV-1 IN binding partner, protein phosphatase 2A (PP2A)-B56 that displays all the key characteristics of a PIC targeting factor (Maertens G.N. 2016). We recently solved the structure of Simian T-cell lymphotropic virus type 1 (STLV-1) intasome in complex with the B56gamma regulatory subunit of PP2A (Barski, M. S. et al, 2020). This has been an immense step forwards towards understanding how PP2A-B56 modulates HTLV-1 infection and how integrase strand transfer inhibitors (INSTIs) currently in use in the clinic to treat HIV-1 patients, but effective at blocking HTLV-1 transmission in tissue culture, binds the integration apparatus of this oncogenic retrovirus (Barski, M.S. et al, 2021). Current investigations in my laboratory are to investigate the mechanism of PP2A-B56 modulation of HTLV-1 infection, integration and integration site selection. 

We are interested in identifying and characterizing host-factors for deltaretroviral INs involved in targeting of integration and post-integration repair, as well as identifying novel targets for therapeutic intervention.

To know more about the lab visit the Maertens' lab webpage.

Research themes.

* Host-retrovirus interaction

* Retrovirus integration site targeting

* Interaction between retroviral INs and target DNA

* Interaction between IN and host chromatin

* HTLV-1 inhibitors

Recent publications.

1.      Schneiderman, B.S., Barski, M.S. and Maertens, G.N. (2022) Cabotegravir, the long-acting integrase strand transfer inhibitor, potently inhibits human T-cell lymphotropic virus type 1 transmission in vitro. Frontiers in Medicine 25;9:889621.

2.      Maertens, G.N., Engelman A.N., and Cherepanov, P. (2022) Structure and function of retroviral integrase. Nature Reviews Microbiology 20(1):20-34.

3.      Barski, M.S., Minnell, J.J. and Maertens, G.N. (2021) PP2A phosphatase as an emerging viral host factor. Frontiers in Cellular and Infection Microbiology 11:725615.

4.      Barski, M.S., Vanzo T., Zhao, X.Z., Smith, J.S., Ballandras-Collas, A., Cronin, N.B., Pye, V.E., Hughes, S. H., Burke Jr., T.R., Cherepanov, P. and Maertens, G.N. (2021)Structural basis for the inhibition of HTLV-1 integration inferred from cryo-EM deltaretroviral intasome structures. Nature Communications 12, 4996.

5.      Barski, M.S., Minnell, J.J., Hodakova, Z., Nans, A., Pye, V., Cherepanov, P. and Maertens, G.N. (2020) Cryo-EM structure of the deltaretroviral intasome in complex the PP2A regulatory subunit B56g. 

6.     Barski, M.S., Minnell, J.J. and Maertens, G.N. (2019) Inhibition of HTLV-1 Infection by HIV-1 First- and Second-Generation Integrase Strand Transfer Inhibitors. Front Microbiol, 10, 1877.

7.      Stockum, A., Snijders, A.P. and Maertens, G.N. (2018) USP11 deubiquitinates RAE1 and plays a key role in bipolar spindle formation. PLoS One, 13, e0190513.

8.      Kirk, P.D., Huvet, M., Melamed, A., Maertens, G.N. and Bangham, C.R. (2016) Retroviruses integrate into a shared, non-palindromic DNA motif. Nat Microbiology, 2, 16212.

9.       Maertens, G.N. 2016. B' protein phosphatase 2A is a functional binding partner of delta-retroviral integrases. Nucleic Acids Research 44:364-76. 

10.       Serrao E., Ballandras-Colas A., Cherepanov P., Maertens G.N.  and Engelman A.E.  2015. Key determinants of target DNA recognition by retroviral intasomes. Retrovirology 12, 39.

11.         Forster, A., Maertens G.N., Farrell P.J. and Bajorek M. 2015. Dimerization of Matrix protein is required for budding of Respiratory Syncytial Virus. J. Virology 89, 4624-4635.

12.         Bajorek M., Caly L., Tran K. C., Maertens G. N., Tripp R. A., Bacharach E., Teng M. N., Ghildyal R. and Jans D. A. 2014. The Thr205 phosphorylation site within Respiratory Syncytial Virus Matrix (M) protein modulates M oligomerization and virus production. J Virology 88, 6380-6393. 

13.         Serrao, E., Krishnan, L., Shun, M.-C., Li, X., Cherepanov, P., Engelman, A. and G. N. Maertens. 2014. Integrase residues that determine nucleotide preferences at sites of HIV-1 integration: Implications for the mechanism of target DNA binding. Nucleic Acids Res 42:5164-76.

14.         Maertens, G. N., N. Cook, W. Wang, S. Hare, S. S. Gupta, V. Pye, O. Cosnefroy, A. Snijders, A. Fassati, A. Engelman, and P. Cherepanov. 2014. Structural basis for nuclear import of splicing factors by Transportin 3 (TNPO3). Proc Natl Acad Sci USA 111:2728-33.

15.        Gupta, S. S., T. Maetzig, G. N. Maertens, A. Sharif, M. Rothe, M. Weidner-Glunde, M. Galla, A. Schambach, P. Cherepanov, and T. F. Schulz. 2013. Bromo and ET domain (BET) chromatin regulators serve as co-factors for murine leukemia virus integration. J. Virol 87:12721-36.

16.        Hare, S., G. N. Maertens, and P. Cherepanov. 2012. 3[prime]-Processing and strand transfer catalysed by retroviral integrase in crystallo. EMBO J. 31: 3020-8.

17.       Cherepanov, P., Maertens, G.N., and Hare, S. Structural Insights into the Retroviral DNA integration apparatus. 2011. Current Opinion in Structural Biology, 21, 249-256. 

18.       Maertens, G.N., Hare, S., and Cherepanov, P. 2010. The mechanism of retroviral integration through X-ray structures of its key intermediates. Nature, 468:326-329. 



Gupta SS, Maetzig T, Maertens GN, et al., 2024, Correction for Gupta et al., "Bromo- and Extraterminal Domain Chromatin Regulators Serve as Cofactors for Murine Leukemia Virus Integration"., J Virol

Schneiderman B, Barski M, Maertens G, 2022, Cabotegravir, the long-acting integrase strand transfer inhibitor, potently inhibits HTLV-1 transmission in vitro, Frontiers in Medicine, Vol:9, ISSN:2296-858X, Pages:1-7

Maertens GN, Engelman AN, Cherepanov P, 2022, Structure and function of retroviral integrase, Nature Reviews Microbiology, Vol:20, ISSN:1740-1526, Pages:20-34

Barski MS, Vanzo T, Zhao XZ, et al., 2021, Structural basis for the inhibition of HTLV-1 integration inferred from cryo-EM deltaretroviral intasome structures (vol 12, 4996, 2021), Nature Communications, Vol:12

Maertens G, Barski MS, Vanzo T, et al., 2021, Structural basis for the inhibition of HTLV-1 integration inferred from cryo-EM deltaretroviral intasome structures, Nature Communications, Vol:12, ISSN:2041-1723, Pages:1-10

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