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UD researchers Jodi Hadden and Juan Perilla have used computer
simulations to learn more about the capsid, or protein shell, that
encloses the genetic blueprint of the hepatitis B virus.
at the University of Delaware, working with colleagues at Indiana
University, have gained new insights into the virus that causes
hepatitis B a life-threatening and incurable infection that afflicts
more than 250 million people worldwide.
The discovery, which was published April 27 in the journal eLife, reveals previously unknown details about the capsid, or protein shell, that encloses the virus genetic blueprint.
Scientists believe that the capsid, which drives the delivery of that
blueprint to infect a host cell, is a key target in developing drugs to
treat hepatitis B.
With hepatitis B, the structure of the capsid has been known for
years, but we wanted to study its motion and its influence on its
surroundings, said Jodi A. Hadden, an independent postdoctoral
researcher in UDs Department of Chemistry and Biochemistry and the lead author of the new paper.
Hadden and the research team used supercomputing resources to perform what are known as all-atom molecular dynamics simulations.
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A computer simulation of the capsid, or protein shell, that encloses the genetic blueprint of the hepatitis B virus and consists of 240 proteins
Molecular dynamics simulations allow researchers to study the way
molecules move in order to learn how they carry out their functions in
nature. Computer simulations are the only method that can reveal the
motion of molecular systems down to the atomic level and are sometimes
referred to as the computational microscope.
In the case of the simulations of the hepatitis B virus, the
researchers found that the capsid is not rigid as previously thought,
but is highly flexible. They also learned that it can distort into an
asymmetric shape, which might allow it to squeeze through an opening
into the nucleus of a cell the virus is infecting.
We think that the capsid might need that ability to distort in order
to correctly package its genetic blueprint and get it into the nucleus
to generate new copies of the virus during the infection process,
Previous research has used experimental microscopes to study the
capsid, which is made up of 240 proteins, but that work hasnt yielded
high-resolution images of the complex structure, said Juan R. Perilla,
assistant professor of chemistry and biochemistry and a co-author of the
It seems clear that the flexibility of the [hepatitis B] capsid is a
limiting factor in the effectiveness of microscopy, he said.
By contrast, the simulations have been able to reveal a more complete
picture of the capsid and how it moves, distorts and interacts with its
environment, Hadden said. Each simulation involves six million atoms.
Jodi Hadden created this depiction of the hepatitis B capsid for UD's annual "Art in Science" exhibition, adding mathematical descriptions of the structure. The notation in the lower left corner indicates that the proteins forming the capsid are arranged in 12 groups of five (pentamers, shown in red) and 30 groups of six (hexamers, in blue) for a total of 240.
"We have all the details down to
the atomic level, she said. You need that to develop a complete
understanding of the molecule and to study drug interactions.
The researchers also found that small triangular openings, or pores,
in the capsid surface are likely the location where its protein tails
poke through, sending a signal that is essential to the infection
We know that the capsid tails have to be exposed to the surface at
some time for the capsid to travel to the cell nucleus, Hadden said.
Its like hailing a taxi.
All the findings have the potential to lead to drug treatments, she
said. For example, if the capsid could be made rigid and unable to
distort or if a way could be found to block the triangular pores in its
surface, the infection process might be halted.
Theres an effective vaccine to prevent hepatitis B, but no cure once
a person is infected. The virus causes severe liver disease, which can
lead to potentially fatal conditions such as cirrhosis and liver cancer.
The paper is available online at eLife, a peer-reviewed, open-access scientific journal for the biomedical and life sciences.
Co-authors, with Hadden and Perilla, are Christopher John Schlicksup,
Balasubramanian Venkatakrishnan and Adam Zlotnick, all of Indiana
University, and the late Klaus Schulten of the University of Illinois at
Urbana-Champaign (UIUC), who pioneered the application of all-atom
molecular dynamic simulations to study complete virus capsids.
The research was supported by UD, through a postdoctoral fellowship
to Hadden, and the National Institutes of Health, through a Center of
Biomedical Research Excellence Grant to Perilla and a Biomedical
Technology Research Resource to Schulten. The computer simulations were
made possible by the Blue Waters project, a joint effort of UIUC and its
National Center for Supercomputing Applications.
Article by Ann Manser; photo by Kathy F. Atkinson; photo illustration by Jeffrey Chase