Finding out how much you weigh is simple–just step on a scale and see the answer within seconds. Weighing ourselves is easy, but how do we weigh the microscopic things in our world that are too small to see? By using mass spectrometry.
Mass spectrometry has been around since the early 20th century, and researchers have gotten very good at measuring the small atoms and molecules that make up our world. Mass spectrometers work by adding a charge to a molecule or atom of interest and then using sophisticated electric fields to accelerate that charged molecule. Because the moving particle’s energy depends on its mass, measurements of the energy allow researchers to deduce that mass. Mass spectrometry works well for atoms and small molecules, but what about biological complexes–like viruses–which are still small, but have masses millions of times larger than a single hydrogen atom?
Conventional mass spectrometers struggle to measure the mass of molecules of intermediate size like viruses; however, researchers in the Jarrold Lab at Indiana University are using a specialized type of mass spectrometry, called Charge Detection Mass Spectrometry (CDMS), which extends the upper mass limit mass spectrometers can measure. The Jarrold Lab was the first to use CDMS to measure the masses of intermediate-sized biological molecules, and remains one of only a few in the world with the capabilities to do so. CDMS has no theoretical mass limit, and current instrumentation has shown accurate mass measurement of viruses up to 55 million times the weight of a single hydrogen atom.
You might be asking yourself, “Do we even care about this intermediate mass range?” The answer is, “Yes!” It turns out that a majority of biologically relevant molecules have masses that fall in this “intermediate” range, including large cellular membrane proteins and viruses. Researchers in the Jarrold Lab are particularly interested in viruses.
Recent Ebola and Zika outbreaks highlight the necessity for a better understanding of malicious viruses, and how to keep them from proliferating. Viruses spread by “hijacking” healthy cells. These “hijacked” cells then begin to create copies of the virus, which then go on to infect other cells. To understand and counter a viral infection, or to harness a virus for other uses, it is important to understand the pathway by which the virus forms, as well as its total mass.
Until recently, the only way to determine the mass of a virus was to make an estimation based on the known masses of the much smaller building blocks that composed that virus. Masses calculated using this method can be inaccurate, because any changes that occur during assembly are not accounted for. The Jarrold Lab, however, has used CDMS to accurately measure both the mass of intact viruses as well as the individual intermediate structuresm which occur as the virus forms. These masses provide information about the assembly of the virus and the timescale in which it occurs, which is useful for developing treatments that combat viral infections.
Measurements of intact viruses have also proven useful for medical treatments that harness the infectious capabilities of viruses and use them for good–without the bad effects of infection; this treatment is referred to as gene therapy. The medicine used in gene therapy is created by removing the malicious components of a virus and loading it with therapeutic components instead. However, it can be difficult to determine to what extent the viruses have been filled with medicine. Recent work by the Jarrold lab has shown that CDMS can accurately determine exactly what percentage of viruses in a gene therapy sample have been completely filled with medicine and how many viruses remain partially filled or empty (shown below). This information is invaluable when determining the dosage requirements for gene therapy. By using CDMS, the Jarrold lab is establishing a new standard in the study of viruses, and will further our ability to both combat malicious viruses and harness them for medical use.
For more information and to keep track of new research from the Jarrold Lab visit their group website.
 E. E. Pierson, D. Z. Keifer, A. Asokan, M. F. Jarrold, Resolving Adeno-Associated Viral Particle Diversity With Charge Detection Mass Spectrometry; Anal. Chem., 2016 ASAP
Edited by Karna Desai and Rachel Skipper