Mechanical engineers might soon be responsible for research on preventing viral infections, according to a visiting scholar from Caltech.
Caltech mechanical engineering postdoctoral student Prashant Purohit gave a presentation on how mechanical engineers might contribute to the general understanding of viruses. By treating the microscopic parts of a virus as mechanical structures, engineers can help determine how viruses operate and how they infect organisms. Approximately 50 UCSB professors and students heard the talk titled “Mechanics of DNA Packaging in Viruses” in the Engineering II pavilion Monday afternoon.
A virus consists mainly of a tiny capsule of genetic material – DNA or RNA. When a virus infects an organism, the genetic material is transferred from the virus into one of the host organism’s cells. The cell unknowingly accepts the virus’ genetic code and follows the code’s instructions to produce more viruses.
Eventually the infected cell dies because it is too busy producing viruses and cannot spend enough energy keeping itself alive. The cell breaks apart, releasing the hundreds of thousands of viruses that it has been making. The released viruses then move out into the organism to infect other cells.
A virus is not really a living thing because it has no ability to reproduce itself – it must find a host to infect and hijack. Even though the virus is not alive, it can still evolve through random mutation and be destroyed by things such as heat so that it can no longer infect cells.
“A virus is a protein shell with the genetic material in the shell,” Purohit said. “The shell is 10-100 nanometers in size and 1-3 nanometers thick.”
For comparison, an average bacterium is about 1,000 nanometers in size yet is still small enough that 1,000 bacteria could be laid end-to-end on the head of a pin. Even though viruses are so small, they have a big effect on the life of the infected cell.
“Once the DNA is inside the cell, it takes over the protein producing machinery and makes more virus,” Purohit said.
In the process of creating more viruses, the cell’s machinery must squeeze string-like DNA into capsules that will eventually become other viruses and leave to infect other cells, Purohit said. This process requires work and is done by a cellular structure called a portal motor. Later, when the new virus infects another cell, the tightly packed DNA launches into the cell like a loaded dart gun being triggered.
“The ejection of DNA into the cell and the portal motor are mechanical processes,” Purohit said. “Is it possible to control that ejection? If we can, we can control the spread of disease.”
Purohit said knowing the structure of the DNA in the virus is important in determining how the virus functions and how it may be defeated.
“Is [DNA] clumped like a ball of string? It turns out it is a very regular arrangement,” Purohit said. “It is in the form of a spool or helix. It is not like a spool of thread where you start winding from the inside. It is an inverse spool – in from the outside.”
The portal motor must force the string of DNA into the cell, where it automatically assumes the coiled shape, Purohit said. This happens because the coiled shape is a very efficient way to force a long string of DNA into a tiny virus capsule.
“This is like forcing 500 meters of Golden Gate bridge [[Bridge]] cabling into the back of a FedEx [[ok]] truck,” Purohit said.
In addition to the problem of getting a lot of stringy DNA into the virus capsule, the portal motor must also fight the DNA’s tendency to repel itself due to electrical charge. This is like pushing two magnets together that are repelling each other.
“At first the packing rate is very high, but falls off as the capsule fills,” Purohit said. “As the container becomes more packed, you have to push harder to get more DNA in.”
Scientists may be able to exploit this force requirement to prevent viral infections.
“If the packing motor of the cell is not powerful enough, the virus will not be packed completely and will not be infectious,” Purohit said.
Purohit said a virus must also carry enough stored energy from the packing to be able to shoot the DNA into the host cell. Infection could be stopped if a force could be delivered that would prevent the virus from ejecting the DNA, like putting a cork into a bottle.
“Mechanics can provide valuable insight into the small-scale biology and possibly [help to] understand diseases,” Purohit said.
Mechanical engineering professor Robert McMeeking said he enjoyed the talk.
“I thought it was fascinating,” McMeeking said. “A lot of viruses, proteins and other important molecules do their thing through shape and force – that’s mechanics.”
George Robert Odette, also a mechanical engineering professor, said the talk added to his previous interest in the topic.
“We’ve heard several talks [like this],” Odette said. “It is a direction that we are going to apply mechanics to biological systems.”
Mechanical Engineering Professor Jeff Moehlis said mechanical analogies of biological systems can be very useful.
“It’s learning the importance of understanding the mechanics of how a virus works,” Moehlis said. “Physicists joke about how well a racehorse will perform. The physicist says, ‘so let’s assume it’s a spherical horse and go from there.'”