Frozen Ebola shows deadly spike
2008-07-10 09:12
Washington - Researchers who have managed
to freeze the Ebola virus and make images of the spike it uses
to infect cells said on Wednesday they hope their work may lead
to a treatment or vaccine for the deadly microbe.
The researchers have a picture of the so-called spike
protein, used by many viruses to get into the cells they
infect.
Ebola's spike protein is concealed, which may help explain
why the virus is so deadly, said Erica Ollmann Saphire, of the
Scripps Research Institute in La Jolla, California, who led the
study.
"It cloaks itself with human carbohydrates," Ollman Saphire
said in a telephone interview.
"It's kind of like Harry Potter wrapped in an invisibility
cloak. But there are three or four little sites peeking out,"
she added.
These may provide a target for a drug or vaccine, or
perhaps an immune-based treatment for Ebola, she said.
"We actually have the roadmap to figure out where the
chinks in its armour are," Ollman Saphire said.
No cure and no vaccine
Ebola haemorrhagic fever is rare, but there is no good
treatment, no cure and no vaccine, and the virus usually kills
between 50% and 90% of its victims.
It is spread when people come into contact with the bodily
fluids of a patient. As with other haemorrhagic fevers, patients
die from dehydration, bleeding, and shock.
The latest outbreak, which ended in February in Uganda, was
unusually mild, killing 37 people out of 149 infected.
A previous outbreak in Uganda in 2000 killed more than half
of 425 people infected and a 2006 outbreak in neighbouring Congo
infected 264 people, killing 187.
While rare, doctors are keen to find a way to treat Ebola
and related viruses such as Marburg.
Ollmann Saphire said it took years to get the virus to
crystallise so an image could be taken.
Researchers used an antibody taken from a survivor of a
1995 outbreak in Zaire, which killed 250 out of 315 people
infected.
Scripps researcher Dennis Burton isolated the
antibody, an immune system protein, from the patient's bone
marrow.
'Fascinating little beast'
What they finally saw surprised them.
The spike protein has two sub-units called gp1 and gp2
which wrap around one another oddly, they reported in the
journal Nature.
"The site is buried under this tree-like canopy of
carbohydrates," said Ollmann Saphire.
This appears to help
cloak it from the body's immune cells.
"It is a fascinating little beast," she said. "It has
evolved all these strategies to achieve its various dastardly
goals while hiding."
Viruses are small organisms, usually with only a handful of
genes. They must hijack a living cell to replicate themselves.
But viruses are also wrapped up tightly, with only one or
two structures that can be affected by the body's
immune-fighting cells, or by drugs.
With Ebola, the spike protein may be the only accessible
target, Ollmann Saphire said.
"Now we can make a movie of all the different gymnastics
that the protein goes through ... in driving the infection,"
she said.