Although the first viruses were beginning to be described in the late 1800s, it wasn't until the mid-20th century that virus discovery flourished. Ever since, virologists and biomedical researchers have investigated the way viruses infect their hosts and replicate, in the hope of developing effective vaccines and treatments. The emergence of novel viruses in the human population, such as SARS-CoV-2 in 2019, shine a spotlight on the need to understand the biological processes underpinning viral infection and the importance of advanced analytical instrumentation.
Electron paramagnetic resonance (EPR) is an important tool that provides insights into the biomolecular structure and dynamics of viruses that other methods, such as X-ray crystallography, cannot achieve. EPR can determine how ordered or disordered proteins are, which is particularly useful in studying the viral membrane proteins that govern their entry into host cells and subsequent reproduction.
For example, the influenza A M2 protein is a membrane-associated protein that plays a role in viral budding - a step in the process of viral reproduction. Site Directed Spin Labeling combined with electron paramagnetic resonance spectroscopy (SDSL-EPR) provides atomic-level understanding of how the protein functions and offers the opportunity to investigate compounds that could inhibit this process, leading to novel strategies for anti-influenza drug design.
SDSL-EPR has also successfully provided new insights into the molecular mechanisms of Hendra (HeV) and Nipah (NiV) viruses - highly pathogenic viruses that emerged from bats in Australia and have caused sporadic outbreaks, with a human mortality rate of 60-75%, over the last 25 years. Studies have used SDSL-EPR to characterize structural transitions within the disordered viral proteins and to understand processes governing both transcription and reproduction. Researchers can also make subtle differentiations between the two viruses using this technique, which could have important implications for the design of inhibitory drug compounds.1
Antiviral drugs are susceptible to resistance, where the virus evolves mechanisms to circumvent the inhibitory effects of the treatment. Double electron-electron resonance (DEER) is a powerful EPR technique allowing researchers to elucidate the mechanisms behind human immunodeficiency virus (HIV) inhibition, to reveal how the virus may mutate and become resistant to anti-HIV drugs.2
The availability of highly sensitive EPR technology is expanding the knowledge of different viral processes. Experiments such as these, using Bruker EPR spectrometers, pave the way for the discovery and development of new antiviral drugs and vaccines.
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1. Kim SS et al. (2015) Cholesterol dependent conformational exchange of the C-terminal domain of the influenza A M2 protein, Biochemistry, 54(49): 7157-7167
2. Martinho M et al. (2013) Assessing induced folding within the intrinsically disordered C-terminal domain of the Henipavirus nucleoproteins by site-directed spin labeling EPR spectroscopy, Journal of Biomolecular Structure and Dynamics, 31:5, 453-471.
3. Liu Z et al. (2015) Pulsed EPR Characterization of HIV-1 Protease Conformational Sampling and Inhibitor-Induced Population Shifts, Phys. Chem. Chem. Phys., 18, 5819-5831