Scientists from UNSW
Sydney and the UK have discovered that the human immunodeficiency virus (HIV) hijacks
a small molecule from the host cell to protect itself from being destroyed by
the host's immune system.
The finding, as well as
details of the new strategy that enabled it, are published as back-to-back
papers in eLife. They identify a new target for antiviral
therapy against HIV and provide a method for testing and measuring new
drugs designed to target the capsid.
UNSW Ph.D. student
Chantal Márquez is involved in both studies and is the first author of the
paper describing the new method.
HIV
forms a protein shell—called a capsid—that shields its genetic material from
host defence mechanisms as it enters the cell and makes its way to the nucleus
to establish infection.
Using a new
single-molecule microscopy technique—developed at UNSW's Single Molecule
Science in the Faculty of Medicine—the research teams found that HIV
specifically incorporates a small molecule from the host cell—inositol
hexakisphosphate—to strengthen its capsid. The host inadvertently provides the
key for the virus infecting it to lock down the protective shell, keeping the
genetic cargo safe until it is released into the nucleus.
"The HIV capsid
falls apart within minutes once it's isolated from the virus," said
Associate Professor Till Böcking, who led the UNSW team involved in both
studies.
"Our strategy lets
us study exactly how a native capsid breaks apart in real-time without taking
it out of the viral membrane."
With the help of
Associate Professor Stuart Turville of the Kirby Institute, the team engineered
viruses with fluorescent tags to monitor the viral capsid using fluorescence
microscopy.
"We can now see the
effect of different molecules on the capsid, and pinpoint precisely
when it cracks open and begins to collapse," says Associate Professor
Böcking.
"Capsids need to be
much more stable inside a cell because the infection
process takes hours, not minutes—so we wanted to find out what keeps it
stable inside a cell," says Dr. David Jacques of Single Molecule Science,
who is an author of both studies.
The researchers found
that inositol hexakisphosphate, which is abundantly present inside
mammalian cells, makes the capsid much stronger, stabilizing it for 10-20
hours.
"It's like a switch.
When you bind this molecule, you stabilize the capsid, and release the molecule
to open it up," explains Associate Professor Böcking.
"The HIV
capsid has been intensively studied, but the question of how it can
simultaneously be both stable and poised to 'uncoat' has been one of the great
unanswered questions in HIV biology," says Dr. Leo James, leader of the
research team at the Medical Research Council Laboratory of Molecular Biology
in Cambridge, UK.
Most of the currently
approved HIV
therapies target enzymes needed at different stages of the virus' life
cycle, but none of them are directed at the HIV capsid. New drug alternatives
could improve the treatment of HIV with reduced toxic effects.
Source: https://medicalxpress.com/news/2018-07-hiv-shielded-immune.html
Abstract Submission: https:/std-hiv-aids.cmesociety.com/abstract-submission
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