Vaccinia (MVA) is a poxvirus, the class of viruses which includes smallpox. They're not fun organisms; the damage they do on cells is shown in the image above. MVA is a complex virus; it's not icosahedron or helical, and there's an intracellular and extracellular version. As far as viruses go, that's pretty complicated, they're generally more simple than this, structure-wise. Additionally, the Helenius group at ETH Zurich has been researching how they act as a trojan horse to cells.
MVA enters a cell by floating up next it, and blebbing it. Blebbing? It's essentially forming an amoeba-like arm and poking and prodding at it. Then, the cell tries to eat the virus, and bam, it's in. Wait, why? If I hear someone knocking at the door, I go look in the peephole. If I see a Jason mask and a shotgun, my first instinct is to not open the door. However, if they're wearing a Papa John's hat and holding a pizza, I'm going to open the door whether or not I ordered it. Do they have a Jason mask and shotgun behind their back? Who cares, pizza!
That's how MVA does its thing. Embedded on MVA's surface is phosphatidylserine (PS). This is present when other cells undergo aptosis, so it signals to the cell that there is going to be cell remnants left for it to eat. Then when it feels the poking and prodding of the blebbing, it starts to eat, and kaboom. That's why I chose an eating analogy. How do we know this is happening? They put different inhibitors onto the virus which will stop this from taking place. You can see from the graph below and the image above, this is effective in stopping the virus from entering. The black bars on the graph are the virus binding to the cell, and the white bars are the cells being infected. ANX5 is one of the inhibitors they tested.
I'd comment more, but uhh, I've told you everything I understand. I should take biochem one day.
Mercer, J., Helenius, A. (2008). Vaccinia Virus Uses Macropinocytosis and Apoptotic Mimicry to Enter Host Cells. Science, 320(5875), 531-535. DOI: 10.1126/science.1155164
Godspeed.
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