We are looking at virus particles on a surface by ordinary scanning electron microscopy. We have noticed that they have strange shapes. They appear elongated and almost faceted, quite different from the spherical shape in a water environment. Has anyone seen any similar effects? I suppose the vacuum could impose such shape changes, just curious if someone has experience of this?
Andreas,
Could these be baculoviridae from an expression system? What size are they and how were they prepared for SEM? Do you have an image to share?
sincerely,
Michael Delannoy
Hi Michael
Thanks for your reply. I'm far from an expert on viruses, but I know these are norovirus particles (containing only the protein shell). They were not prepared for SEM at all. We measure how viruses interact with lipid membranes on sensor surfaces. It was just by chance we put a sample into the SEM after it had been used to detect virus binding. That's when we saw the viruses. They slowly disappeared while exposed to the electron beam as expected for organic material. The size should be 50 nm I believe and that is approximately what they looked like. It's just the shape which surprised us.
Unfortunately I feel that I cannot distribute the data at this point since it is material to be published. Sorry about that, I realize it would be helpful...
Best regards,
Andreas
Andreas,
Perhaps try some negative stain and TEM viewing?
cheers,
Michael Delannoy
I've worked with viruses under TEM. For these we deposit them on the grid for about 2 mins and then negatively stain with 2%UA for 2 mins before loading the samples. I have seen long, thin baculovirus and perfect spherical icosahedral viruses. However many of the particles are also damaged. I would not expect the vacuum to damage the particles at all. You could also try AFM to detect interaction on your surface.
Dear Andreas,
I understand (from your reply to Michael B. Dahlin) that you are self-assembling the capsid protein only without the genome. When you do that, depending on the conditions you are using (ionic strength and pH) you can expect the formation of different polymorphs of empty capsids. This is, you can form capsids that resemble the virión, multishell capsids, elongated capsids and tubes. This have been studied for the self-assembly of the capsid protein without the genome of the CCMV virus, where a phase diagram has been constructed to explain the formation of different structures. See the following references:
1. Lavelle, L., M. Gingery, M. Phillips, W. M. Gelbart, C. M. Knobler, R. D. Cadena-Nava, J. R. Vega-Acosta, L. A. Pinedo-Torres, and J. Ruiz-Garcia. "Phase Diagram of Self-assembled Viral Capsid Protein Polymorphs. The Journal of Physical Chemistry B 113, no. 12 (2009): 3813-3819.
2. Vega-Acosta, J. R., Ruben D. Cadena-Nava, William M. Gelbart, Charles M. Knobler, and Jaime Ruiz-García. "Electrophoretic Mobilities of a Viral Capsid, Its Capsid Protein, and Their Relation to Viral Assembly." The Journal of Physical Chemistry B 118, no. 8 (2014): 1984-1989.
Dear Jaime
Thanks a lot, this sounds very useful. I will definitely check those references.
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