Imperial College London


Faculty of MedicineDepartment of Medicine

Senior Lecturer



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




, Medical SchoolNorfolk 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 delta-retrovirus 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. 

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. 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). Recently, 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. We are interested in identifying and characterizing host-factors for lenti- and other retroviral INs involved in targeting of integration and post-integration repair.

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 that displays all the key characteristics of a PIC targeting factor (Maertens G.N. 2016). Current investigations in my laboratory are to structurally characterize the interaction and to investigate the contribution of this host factor to integration site selection.

Research themes.

* Host-retrovirus interaction

* Retrovirus integration site targeting

* Interaction between retroviral INs and target DNA

* Interaction between IN and host chromatin

Recent publications.

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

2.         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.

3.         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.

4.         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. 

5.         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.

6.         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.

7.        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.

8.        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.

9.       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. 

10.       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. 



Kirk PDW, Huvet M, Melamed A, et al., 2017, Retroviruses integrate into a shared, non-palindromic DNA motif, Nature Microbiology, Vol:2, ISSN:2058-5276

Maertens GN, 2016, B '-protein phosphatase 2A is a functional binding partner of delta-retroviral integrase, Nucleic Acids Research, Vol:44, ISSN:0305-1048, Pages:364-376

Foerster A, Maertens GN, Farrell PJ, et al., 2015, Dimerization of Matrix Protein Is Required for Budding of Respiratory Syncytial Virus, Journal of Virology, Vol:89, ISSN:0022-538X, Pages:4624-4635


Quinn K, Winston A, Kaye S, et al., 2016, Slow emergence of resistance to C34-PEG4-Chol; a novel HIV fusion inhibitor, WILEY-BLACKWELL, Pages:29-29, ISSN:1464-2662

Thesis Dissertations

McCallin, 2016, The Regulation of HTLV-1 Integration by a Host Co-Factor

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