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.
Reviewing Editor
- Wesley I Sundquist, University of Utah School of Medicine, United States
Version history
- Received: January 23, 2018
- Accepted: May 29, 2018
- Accepted Manuscript published: May 31, 2018 (version 1)
- Version of Record published: July 10, 2018 (version 2)
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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- Microbiology and Infectious Disease
- Structural Biology and Molecular Biophysics
Genetic diversity is a hallmark of RNA viruses and the basis for their evolutionary success. Taking advantage of the uniquely large genomic database of SARS-CoV-2, we examine the impact of mutations across the spectrum of viable amino acid sequences on the biophysical phenotypes of the highly expressed and multifunctional nucleocapsid protein. We find variation in the physicochemical parameters of its extended intrinsically disordered regions (IDRs) sufficient to allow local plasticity, but also observe functional constraints that similarly occur in related coronaviruses. In biophysical experiments with several N-protein species carrying mutations associated with major variants, we find that point mutations in the IDRs can have nonlocal impact and modulate thermodynamic stability, secondary structure, protein oligomeric state, particle formation, and liquid-liquid phase separation. In the Omicron variant, distant mutations in different IDRs have compensatory effects in shifting a delicate balance of interactions controlling protein assembly properties, and include the creation of a new protein-protein interaction interface in the N-terminal IDR through the defining P13L mutation. A picture emerges where genetic diversity is accompanied by significant variation in biophysical characteristics of functional N-protein species, in particular in the IDRs.
