Download Model of Wild Type (3A) Picornovirus Infection The Secretory

“Bad Roommate!”
3A Protein: An Inhibitor of ER to Golgi Traffic
Valders High School SMART Team: Grace L. Ebert, Nicole C. Maala, Joe P. Nagel, Paige N. Neumeyer, Stacie L. Pearson, Gavin X. Schneider,
Luke J. Schuh, Kayla N. Walsh, Emily N. Weyker, Alyssa L. Yindra
Instructor: Mr. Joseph S. Kinscher Mentor: William T. Jackson, Ph. D., Medical College of Wisconsin
2010-2011 Valders SMART Team
Abstract:
Acute respiratory illnesses (colds), hepatitis, poliomyelitis, and livestock diseases are caused by members of the viral family Picornaviridae. The common cold is the most prevalent infectious disease in humans and
results in major economic impact through loss of productivity and strain on healthcare systems. 3A is a membrane protein produced by these viruses that is necessary for forming viral replication complexes. 3A is an attractive target
in strategies to combat these diseases. Normally, cells communicate using the secretory pathway. Proteins from the endoplasmic reticulum (ER) enter the Golgi apparatus where they are processed and packaged into vesicles for
secretion. When cells are infected by viruses, the cells produce cytokines and display viral peptides on major histocompatibility complex molecules to induce an immune response. Picornovirus 3A inhibits the host cell immune
response by interrupting this communication pathway. 3A inhibits cellular secretion and promotes the remodeling of the endoplasmic reticulum membranes into replication complexes for viral RNA synthesis. This is believed to
occur through 3A binding to Golgi-specific-brefeldin-factor 1, which inhibits protein transport. Studies have found that some amino acids in the 3A protein have been evolutionarily conserved and therefore may be important to 3A
function. Knowing the significance of these amino acids could lead to an attenuated vaccine encoding a mutated form of 3A.
3A Protein Model
Model of Wild Type (3A) Picornovirus Infection
The Problem: The common cold, hepatitis, and livestock
viruses impact health and economic systems globally. In
2011, South Korea experienced a devastating epidemic of
hoof-and-mouth disease. More than 2 million animals
were culled to prevent the spread of the disease, costing
the country 1.4 billion dollars. In humans, the common
cold is the most prevalent infectious disease resulting in
loss of productivity which is estimated to cost the U.S.
economy 25 billion dollars each year. When infected, cells
cannot secrete proteins that would allow an immune
response to prevent the spread of the disease. The viral
protein 3A could be targeted to combat these diseases. The
3A protein is critical for forming viral replication complexes
in host cells. Scientists are researching a way to inhibit 3A
with the objective of creating drugs to inhibit the protein
or a vaccine containing a mutant form of 3A.
The Secretory Pathway
nucleus
Threonine (T14)
Virus- wild type
Infection
ER
based on 1ng7.pdb
3A
Golgi
Fig. 2
Changing the amino acid sequence of viral protein 3A
could provide an attenuated vaccine (Fig. 2). The 3A-2
mutant contains a serine insertion between threonine
(T14) and serine (S15). This disrupts the ability of the
3A protein to inhibit endoplasmic reticulum (ER) to
Golgi complex communication.
Vesicles
MHCs
Weakened
Cytokines
Immune “Alerts”
3A inhibits cell protein secretion and vesicles will
form from the ER membranes. These vesicles
will serve as complexes for viral RNA replication.
protein
Serine (S15)
Like a bad roommate trashes an apartment 3A destroys the host cell. The cell lyses, dies,
and newly formed viruses are released for
further infection.
rough ER
Model of Mutant (3A-2) Picornovirus Infection
Secretory
vesicle
Virus- mutant
White Blood Cell
ribosome
Control
wild type 3A
S.S. Choe et al. Virology 337 (2005) 18-29
ER
3A
smooth
ER
Golgi
Golgi
Fig. 1
Cells communicate with each other using the secretory
pathway, in which proteins from the endoplasmic
reticulum (ER) enter the Golgi apparatus and are packaged
into vesicles for secretion (Fig. 1). Using this pathway, cells
produce cytokines and display viral peptides on major
histocompatibility complex molecules (MHCs) to induce an
immune response.
Fig. 3
Secreted alkaline phosphatase (SEAP) is used to
measure protein secretion in eukaryotic cells (Fig. 3).
The wild type 3A protein reduced cell secretion by 80
percent after 30 minutes. The 3A-2 mutant
demonstrates that cell protein secretion is reduced by
only 40 percent after 30 minutes and thus could lead
to an attenuated vaccine.
Infection
protein
vesicle
3A-2 mutant
MHCs
Biological Significance: Further research of the
Immune “Alerts” Cytokines
The 3A-2 mutant is not effective at reducing protein
secretion - the infected cell produces cell-signaling
protein molecules (i.e. cytokines) to initiate an
immune response.
MHCs present a fragment of the
antigen (virus) to T lymphocytes, while
cytokines activate other white blood
cells. Both alert the immune system
to destroy infected cells - interrupting
viral reproduction.
3A protein may lead to the development of drugs
targeting 3A or an attenuated vaccine encoding a
mutant 3A. This could potentially lead to treatment or
prevention of infectious diseases such as the common
cold and hoof and mouth disease.
References:
1. Belov et al. Cell Cycle. 6:1. 2007, 36-38
2. Choe et al. Virology . 337. 2005, 18-29
A SMART Team project supported by the National Institutes of Health (NIH)-National Center for Research Resources Science Education Partnership Award (NCCR-SEPA).
3. Hancocks, CNN. January 21, 2011
4. Strauss et al. Journal of Molecular
Biology. 330. 2003, 225-234