Koromyslova et al., 2015, sought out study whether citrate would have any impact on the Norovirus GII. 10 P-domain which protrudes out from these particles' capsid shown in image below.
Researchers treated Norovirus-like particles (VLPs) with similar structures to that of Norovirus with varying levels of citrate buffer for 30 minutes at room temperature. The objective of this was to detect any possible structural changes in the virus to then establish any potential vulnerabilities in the virus. The varying amounts of buffer were 0mM (control), 0.49mM, 1.95mM, 3.91mM, 7.85mM, 15.63mM, 31.25mM, 62.50mM and 125.00mM. The buffer concentrations between and including 0.49mM and 7.85mM were found to be indistinguishable from the control group (0mM of citrate buffer). Thus, concluding that those concentrations did not have any effect on the structure of the virus. The citrate buffer concentration 15.63mM had a slight structural change in the virus (the outer protruding 'spikes' on the virus were surrounded by a couple of rings). The citrate concentration of 62.50mM resulted in the most structural changes causing the virus to exhibit multiple rings around the protruding spikes as well as a substantial increase in width and diameter of the virus. The concentration of 125.00 showed decreased structural changes as compared to 62.50mM. The control VLP's diameter was ~42 to 44nm, and the experimental VLP's treated with 62.50mM exhibited a diameter of ~46 to 49nm (the greatest diameter exhibited).
Once the VLP's were exposed to a citric buffer, the VLP's were analyzed using ELISA (a assay which uses monoclonal and polyclonal antibodies to identify a particle). The VLP's exposed to 0.25mM to 7.81mM citrate buffer, resulted in low polyclonal antigen binding indicative from the low optical density (OD490= 0.15). These results were similar to those seen in the control group (0mM citrate buffer). The optical density continuously rose with increasing amounts of citrate buffer. The max optical density was reached at 62.50mM citrate buffer (OD490= 2.20). The same results presented when analyzes with monoclonal antigens; the control group's OD450=0.11 and the peak optical density was reached at 62.50mM citrate buffer (OD450= 3.60). As citrate buffer increased (leveled off at 62.50mM, increasing amounts of antigens were able to bind to the virus, thus promoting viral death.
An x-ray crystallography was conducted to see whether lemon juice and disinfectant citrate would bind to the P domain on the Norovirus. There are different subtypes of P domains on the Norovirus (i.e., P1 subdomain and P2 subdomain) which differ from another structurally (i.e., different amounts of ∂-helixes and ß-sheets). The results of the x-ray crystallography displayed that the Norovirus and disinfectant complex diffracted to 1.78 Å resolution which was also observed in the lemon juice and Norovirus complex. It was conclusive that citrate disinfectant and lemon juice were capable of binding to the P domain on Norovirus.
The implications for this study are that citrate buffer at a max concentration of 62.50mM is capable of structurally changing the Norovirus (increasing its diameter and width). This structural change allows for antibodies to easily access the P domain, thus rendering the virus useless. In addition to this, it was also found that citrate bound to the histo-blood group antigen binding pocket, attachment factors for Norovirus.
Though this study shows promise for potential future Norovirus treatment, further studies should be conducted particularly on the effects of lemon juice on Norovirus to further conclude lemon juice as a treatment.
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References
Koromyslova, A., White, O., & Hansman, G. (2015). Treatment of Norovirus Particles with Citrate. Elsevier, 199-204.
Images in order of appearance
http://jvi.asm.org/content/85/13/6687.figures-only
Koromyslova, A., White, O., & Hansman, G. (2015). Treatment of Norovirus Particles with Citrate. Elsevier, 199-204.
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