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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- Microbiology and Infectious Disease
Chlamydia trachomatis is an obligate intracellular bacterial pathogen with a unique developmental cycle. It differentiates between two functional and morphological forms: the elementary body (EB) and the reticulate body (RB). The signals that trigger differentiation from one form to the other are unknown. EBs and RBs have distinctive characteristics that distinguish them, including their size, infectivity, proteome, and transcriptome. Intriguingly, they also differ in their overall redox status as EBs are oxidized and RBs are reduced. We hypothesize that alterations in redox may serve as a trigger for secondary differentiation. To test this, we examined the function of the primary antioxidant enzyme alkyl hydroperoxide reductase subunit C (AhpC), a well-known member of the peroxiredoxins family, in chlamydial growth and development. Based on our hypothesis, we predicted that altering the expression of ahpC would modulate chlamydial redox status and trigger earlier or delayed secondary differentiation. Therefore, we created ahpC overexpression and knockdown strains. During ahpC knockdown, ROS levels were elevated, and the bacteria were sensitive to a broad set of peroxide stresses. Interestingly, we observed increased expression of EB-associated genes and concurrent higher production of EBs at an earlier time in the developmental cycle, indicating earlier secondary differentiation occurs under elevated oxidation conditions. In contrast, overexpression of AhpC created a resistant phenotype against oxidizing agents and delayed secondary differentiation. Together, these results indicate that redox potential is a critical factor in developmental cycle progression. For the first time, our study provides a mechanism of chlamydial secondary differentiation dependent on redox status.
