Discover the maturation and spread of dengue virus

Purdue University biologists have identified why the dengue virus must undergo structural transformation to mature in host cells, and how important these changes are. for the ability of the virus to infect other host cells.

This finding covers all viruses of the family flaviviruses that are involved in many dangerous insect-spreading diseases such as dengue fever, West Nile, yellow fever or St. encephalitis. Louis. Dengue is very common in Southeast Asia, Central America and South Africa. The virus that causes dengue fever spreads through mosquitoes that affects up to 50 million people and causes 24,000 deaths each year, mainly in the tropics.

Researchers have described in detail the essential changes that occur when the virus gathers their organs and when they move from inside to outside the host cell before spreading it to the cells. other. The parts of the virus that are exposed to the environment have an increase in acidity as they carry out the mechanism of excretion. This modified acidity plays a vital role in the maturation process of the virus. Michael Rossmann, professor of biological sciences, said: 'This is probably the most thorough understanding of virus maturation.'

The study was conducted in collaboration with two laboratories at Purdue, one run by Professor Rossman and the other by Jue Chen, an assistant professor of biological sciences. Participating in the study was I-Mei Yu, a postdoctoral researcher who worked with Chen - and Long Li - a doctoral student with Professor Rossman.

The results are explained on the next two articles published Friday, March 28, 2008 in Science. The authors of two articles include Yu, Li, Rossmann, Chen and Richard J. Kuhn - professor and Dean of Purdue University's Department of Biological Sciences.

Professor Rossman said that while the virus pathway enters a relatively well-studied new host cell, the path that the virus exits from the host cell initially has not been thoroughly understood. He said: ' These two articles want to focus on this path and compare the differences between the two paths'.

The virus has passed through the cells inside the cell called the endoplasmic reticulum and the Golgi network. When immature, the virus parts cannot combine with cell membranes, so they cannot affect host cells. However, according to Chen, when the virus is mature, it can combine with the cell membrane to allow viral parts to spread to other host cells.

The picture above describes dengue virus. On the top left is a low-temperature electron micrograph, on the right are images that reproduce the maturation process of virus components as they move through the host cell. Purdue University biologists have determined why the virus undergoes structural transformation to mature in host cells, and how important these changes are for potentials. The ability of the virus to infect other host cells. Other images detail the structure of the virus and the essential components of the two proteins linked together with the precursor membrane protein and shell protein.
(Photo: Purdue University)

Chen said: 'There are many membranes in the Golgi network so immature viruses are surrounded by these membranes. In fact, the environment of the pathway is very similar to the environment that the virus encounters when it invades and harms a new host cell. Therefore, the question is why does the virus not combine with the cell membrane when escaping? '

Scientists have identified the key role of the change in acidity as mature viruses move through the cell cavities. Rossman said: 'We have known the phenomenon of acid concentration changes, but its influence on the maturation process of the virus has not been discovered until these findings are obtained'.

When a part of the virus grows along its path in the host cell, it changes the protein structure itself in the outer shell. Yu simulated the Golgi network environment in test tubes that allowed researchers to understand the process of changing the structure of the virus as the concentration of acid increased. The surface of each part of the virus contains up to 180 component copies that make up two interlinked proteins that have the precursor membrane protein and shell protein.

The precursor membrane protein prevents immature viruses from combining with cell membranes by coating the binding point on the membrane protein. In adulthood, an enzyme called furin cuts off the link between the two proteins, exposing it to the membrane binding point and allowing the virus to bind to the cell membrane.

However, Yu also found that the membrane protein precursor remained dormant until the virus was ready to escape from the original host cell. The researchers used a technique called low-temperature electron microscopy to get a more detailed view of what is going on inside the virus.

Chen said: 'The membrane protein precursor remains on the surface of the virus even if the enzyme has separated two proteins. This is an important step because the virus is mature, but still cannot be combined with the cell membrane until it exits its host cell. ' The scientists also found that the environment needs to be acidic before the enzyme detaches two proteins. They also studied the structure to find out why it is necessary to have an increasing acidity.

Li used fruit fly cells to produce large amounts of binding proteins from which researchers could learn by X-ray crystallography. Using the crystallography method, researchers can visualize and study the combined structure of precursor membrane proteins and shell proteins.

Rossman said: 'A deeper understanding of this structure allows us to know why immature viruses cannot be combined with cell membranes. Basically, researchers want to find ways to treat or prevent the effects of the virus. But to do that, we must first know how the virus works, how it matures and how it spreads. '

To create a complex of two proteins, Li first had to replace the insoluble transmembrane region of the protein with a soluble fraction - an essential step in using fruit fly cells to produce proteins. He also had to modify the protein by removing the points of the furin enzyme that normally clung to, preventing proteins from being separated.

The precursor protein membrane is about 50 nanometers wide (less than 1 meter billions of times), the shell protein is about 3 nanometers wide, nearly the size of an atom. One nanometer is the size of 10 hydrogen atoms attached together.

Later studies will focus on the process of changing the structure of the virus at a more detailed level.