8 research outputs found
Novel Escape Mutants Suggest an Extensive TRIM5α Binding Site Spanning the Entire Outer Surface of the Murine Leukemia Virus Capsid Protein
After entry into target cells, retroviruses encounter the host restriction
factors such as Fv1 and TRIM5α. While it is clear that these factors target
retrovirus capsid proteins (CA), recognition remains poorly defined in the
absence of structural information. To better understand the binding interaction
between TRIM5α and CA, we selected a panel of novel N-tropic murine
leukaemia virus (N-MLV) escape mutants by a serial passage of replication
competent N-MLV in rhesus macaque TRIM5α (rhTRIM5α)-positive cells using
a small percentage of unrestricted cells to allow multiple rounds of virus
replication. The newly identified mutations, many of which involve changes in
charge, are distributed over the outer ‘top’ surface of N-MLV CA,
including the N-terminal β-hairpin, and map up to 29 Ao apart.
Biological characterisation with a number of restriction factors revealed that
only one of the new mutations affects restriction by human TRIM5α,
indicating significant differences in the binding interaction between N-MLV and
the two TRIM5αs, whereas three of the mutations result in dual sensitivity
to Fv1n and Fv1b. Structural studies of two mutants show
that no major changes in the overall CA conformation are associated with escape
from restriction. We conclude that interactions involving much, if not all, of
the surface of CA are vital for TRIM5α binding
Trans-species polymorphism in humans and the great apes is generally maintained by balancing selection that modulates the host immune response
HIV-1 uses dynamic capsid pores to import nucleotides and fuel encapsidated DNA synthesis
© 2016 Macmillan Publishers Limited. All rights reserved. During the early stages of infection, the HIV-1 capsid protects viral components from cytosolic sensors and nucleases such as cGAS and TREX, respectively, while allowing access to nucleotides for efficient reverse transcription. Here we show that each capsid hexamer has a size-selective pore bound by a ring of six arginine residues and a â molecular iris' formed by the amino-terminal β-hairpin. The arginine ring creates a strongly positively charged channel that recruits the four nucleotides with on-rates that approach diffusion limits. Progressive removal of pore arginines results in a dose-dependent and concomitant decrease in nucleotide affinity, reverse transcription and infectivity. This positively charged channel is universally conserved in lentiviral capsids despite the fact that it is strongly destabilizing without nucleotides to counteract charge repulsion. We also describe a channel inhibitor, hexacarboxybenzene, which competes for nucleotide binding and efficiently blocks encapsidated reverse transcription, demonstrating the tractability of the pore as a novel drug target