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ERC

HIVINNATE Report Summary

Project ID: 339223
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Mid-Term Report Summary - HIVINNATE (Characterisation and Manipulation of Primate Lentiviral Interactions with Innate Immunity)

HIV-1 virions contain a cone shaped core made of capsid (CA) protein arranged into hexameric and pentameric capsomeres. 150 hexamers and 12 pentamers come together to form the cone shaped HIV-1 core that contains the viral nucleic acid and viral enzymes required for viral replication. Our central hypothesis, developed during this programme, is that, contrary to textbook dogma, the viral core does not dissolve on entry into the cytoplasm prior to or during DNA synthesis. Rather, the core acts as a molecular machine protecting the viral nucleic acids while simultaneously regulating the processes of viral DNA synthesis, nuclear import and integration targeting. We believe that previous reports describing cytoplasmic uncoating are measuring the majority of virus particles that do not achieve an infection event. Rather the viral particles that do not make it are degraded, dismantled or otherwise destroyed by the cells defensive activities. We hypothesise that, throughout the journey from the cell exterior to the nucleus, the CA protects the viral nucleic acid from being degraded and from activating pattern recognition receptors. Our hypothesis is supported by 2 transformative studies published in Nature in 2013 and 2016. The first demonstrates that two CA binding cofactors, namely cyclophilin A (CypA) and control of polyadenylation specificity factor 6 (CPSF6) are required for HIV-1 evasion of innate immune DNA sensors in MDM. In the absence of CypA or CPSF6 recruitment to CA, HIV-1 infection activates viral DNA dependent innate sensing that triggers type 1 interferon production in MDM leading to complete suppression of replication. An important question that arose from this work was, if the CA core remains intact during viral DNA synthesis, how do the nucleotides that fuel this process access the polymerase complex inside the core? This question led to our second key observation. Examination of the hexameric capsomere structures revealed that they are electrostatic channels that transport nucleotides into the viral core. Critically, nucleotide import is regulated by a molecular iris formed by the CA beta hairpin that opens and closes to control access to the CA channel. Breaking the channel, with either mutations in the electrostatic channel core (R18G), or in the molecular iris mechanism (H12Y) prevent viral DNA synthesis, but the mutant viruses form apparently normal viral particles with apparently normal cores. These paradigm shifting observations explain how cofactors and antiviral drugs that recruit to the outside of the core can regulate the DNA synthesis going on inside the core through regulating the electrostatic channel in a temporal and position specific way within the cell. Understanding the mechanisms HIV-1 uses to evade innate immunity has allowed us to develop three new classes of new antiviral inhibitors. These include CypA inhibitors that prevent CypA recruitment leading to activation of innate immunity, CA binding inhibitors that prevent recruitment of cofactors and channel inhibitors that block activity of the electrostatic channel. We are now examining the mechanisms by which viral DNA is sensed when cofactor interactions are disturbed, we are seeking to understand the molecular details of the allosteric mechanism by which CA regulates viral DNA synthesis through regulating the electrostatic channel and how viral organisation within the CA contributes to the processes of DNA synthesis and uncoating.

Contact

Giles MACHELL, (European Research and Innovation Office)
Tel.: +44 20 3108 9375
E-mail
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