IP6 is an HIV pocket factor that prevents capsid collapse and promotes DNA synthesis
- Medical Research Council Laboratory of Molecular Biology, United Kingdom
- University of New South Wales, Australia
- University College London, United Kingdom
Abstract
The HIV capsid is semi-permeable and covered in electropositive pores that are essential for viral DNA synthesis and infection. Here we show that these pores bind the abundant cellular polyanion IP6, transforming viral stability from minutes to hours and allowing newly synthesised DNA to accumulate inside the capsid. An arginine ring within the pore coordinates IP6, which strengthens capsid hexamers by almost 10°C. Single molecule measurements demonstrate that this renders native HIV capsids highly stable and protected from spontaneous collapse. Moreover, encapsidated reverse transcription assays reveal that, once stabilised by IP6, the accumulation of new viral DNA inside the capsid increases > 100-fold. Remarkably, isotopic labelling of inositol in virus producing cells reveals that HIV selectively packages over 300 IP6 molecules per infectious virion. We propose that HIV recruits IP6 to regulate capsid stability and uncoating, analogous to picornavirus pocket factors.
Data availability
Diffraction data have been deposited in PDB under the accession code 6ERM, 6ERN and 6ES8.
Article and author information
Author details
Funding
Medical Research Council (U105181010)
- Leo C James
Wellcome
- Leo C James
National Health and Medical Research Council (339223)
- Till Böcking
National Health and Medical Research Council (GNT1036521)
- David A Jacques
Wellcome (206248/Z/17/Z)
- William A McEwan
Wellcome
- Gregory J Towers
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2018, Mallery et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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IP6 is an HIV pocket factor that prevents capsid collapse and promotes DNA synthesis
eLife 7:e35335.
https://doi.org/10.7554/eLife.35335
Further reading
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- Microbiology and Infectious Disease
- Structural Biology and Molecular Biophysics
Structural and biophysical studies help to follow the disassembly of the HIV-1 capsid in vitro, and reveal the role of a small molecule called IP6 in regulating capsid stability.
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- Biochemistry and Chemical Biology
- Microbiology and Infectious Disease
Birnaviruses are a group of double-stranded RNA (dsRNA) viruses infecting birds, fish, and insects. Early endosomes (EE) constitute the platform for viral replication. Here, we study the mechanism of birnaviral targeting of EE membranes. Using the Infectious Bursal Disease Virus (IBDV) as a model, we validate that the viral protein 3 (VP3) binds to phosphatidylinositol-3-phosphate (PI3P) present in EE membranes. We identify the domain of VP3 involved in PI3P-binding, named P2 and localized in the core of VP3, and establish the critical role of the arginine at position 200 (R200), conserved among all known birnaviruses. Mutating R200 abolishes viral replication. Moreover, we propose a two-stage modular mechanism for VP3 association with EE. Firstly, the carboxy-terminal region of VP3 adsorbs on the membrane, and then the VP3 core reinforces the membrane engagement by specifically binding PI3P through its P2 domain, additionally promoting PI3P accumulation.
