"Science doesn't yet fully understand exactly how neutralizing antibodies work," said Michael Rossmann, the Hanley Distinguished Professor of Biological Sciences in Purdue's College of Science. "This work has shown precisely where the antibody binds to the virus, and we now have a theory for how it interacts with the virus to disarm it. Perhaps we are starting to understand why this particular antibody can inhibit the infectivity of the virus, which is important to understand if a vaccine is going to be developed."
Purdue worked with researchers from the Washington University School of Medicine in St. Louis.
West Nile belongs to a family of viruses known as flaviviruses, which includes a number of dangerous insect-borne disease-causing viruses. The antibody attaches to a protein called an E protein, for envelope protein, which makes up the virus's outer shell. There are 180 copies of E proteins symmetrically arranged in 60 sets of three, forming a geometric shape called an icosahedron, which is made up of triangular facets.
The researchers, however, were surprised to discover that this antibody recognizes only two of the E proteins in each set of three, said Bärbel Kaufmann, a postdoctoral research associate working in the Rossmann lab.
"This finding was very unusual," she said. "If the E proteins really are the same, why doesn't the antibody bind to all of the E proteins? This kind of asymmetry, where you have two proteins binding and one not binding, has not been seen before."
The researchers theorize that, although chemically identical, these E proteins exist in different environments relative to each other and might, therefore, have slightly different structures, said Richard J. Kuhn, a professor and head of Purdue's Department of Biological Sciences.
The findings were detailed in a research paper appearing last week in Proceedings of the National Academy of Sciences.
Researchers know that when the virus infects a host cell, it interacts with the cell membrane in such a way that it is swallowed up by the membrane and enters the cell as an "endocytotic particle." The Purdue researchers have now developed a theory for the mechanism behind the interaction and will test it in further research, Rossmann said.
Once the virus penetrates the host cell, the viral membrane fuses with an internal membrane in the cell. This process causes the virus particle to empty its contents inside the cell and leads to infection.
To study how the antibodies and E proteins attach, Kaufmann first separated the antibody's tail end from its two grasping, fingerlike structures called "antigen binding fragments."
"We don't want to handle the whole molecule, so we cut off these antigen binding domains and then combined them with the virus, forming the virus-antibody complex," Kaufmann said.
The researchers then used an electron microscope and a process called cryoelectron microscopy to take detailed pictures of this complex. Then they computed a three-dimensional model based on these pictures showing the outstretched antigen binding fragments attached to the virus particle.
The E proteins in one triangular segment of the icosahedron are not all positioned the same way relative to each other and to the various "axes" that define the icosahedron. This difference in position appears to be crucial in the binding process.
The antibody is called a monoclonal antibody because it recognizes only a single binding site on the E protein. Each E protein has three "domains," or well-defined, folded segments. The third domain has a structure commonly seen in molecules that attach to proteins to perform a specific function in cells. The grasping antibody segment used in the study attaches only to the third domain of the E proteins.
"One of the three E proteins in the triangular segment fails to be recognized by the antibody because its third domain crowds together with other E proteins on the viral surface," Kuhn said.
Researchers at the Washington University School of Medicine have shown through experiments that the antibody does not prevent the virus from attaching to human cells, so it is likely that the antibody works by preventing the fusion step from occurring.
Purdue researchers had previously theorized that before the virus fuses, the E protein undergoes dramatic structural repositioning and that the antibodies might inhibit those changes, preventing infection.
"We have a model for understanding how this inhibition process may work," Rossmann said. "We think it's likely that the antibody blocks the positional changes needed for the E protein before fusion, in effect preventing the virus from infecting the cell by jamming the mechanism."
After infection, it takes a few days to a few weeks for the body to make the antibodies, or enough of them to fend off infection.
"If the virus is fast enough, you become sick," Kuhn said. "But if you were vaccinated, you might already have enough antibodies to prevent infection, and that's why these findings are ultimately important. If we understand the mechanism of neutralization, then we might be able to design more effective vaccines."
West Nile virus causes a potentially fatal illness and has infected thousands of people in the United States over the past five years, killing more than 700 people in that time frame.
The research is funded by the National Institutes of Health. Future work could focus on confirming the theoretical model for the antibody's neutralizing mechanism.
"If our theory is right and the antibody binding blocks the E protein's transformation so that fusion can't take place, then we should be able to capture the intermediate stages of this rearrangement of the E protein prior to fusion," Kaufmann said.
The paper was authored by Kaufmann, Purdue electron microscopist Paul R. Chipman, Purdue associate research scientist Wei Zhang, Kuhn and Rossmann, and three researchers from the Washington University School of Medicine: Grant E. Nybakken, a graduate student in the Department of Pathology and Immunology; Michael S. Diamond, an assistant professor in the departments of Medicine, Molecular Microbiology, Pathology and Immunology; and Daved H. Fremont, an associate professor of pathology and immunology, biochemistry and molecular physics.
Writer: Emil Venere, (765) 494-4709, email@example.com
Sources: Michael Rossmann, (765) 494-4911, firstname.lastname@example.org
Richard J. Kuhn, (765) 494-1164, email@example.com
Barbel Kaufmann, firstname.lastname@example.org
Purdue News Service: (765) 494-2096; email@example.com
Emil Venere | EurekAlert!
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Health and Medicine
19.07.2018 | Earth Sciences
19.07.2018 | Power and Electrical Engineering