Male Audience: Or does it do any genetic editing to the viral genome itself?
Erica Ollmann Saphire: Oh that is another question. We wanted to keep cycles of replication going to see if it had a proof reading function. We don’t know. We love to do those kind of studies.
Male Audience: So I have a second question about this RNA binding towards by the protein at the end and also on the side. So, I guess you mentioned that chemical nature is totally different, one is hydrophobic and another is electrostatic. Which one actually dominants – I mean if you analyze the binding affinity – obviously the cap end binding has a disadvantage because it needs each strand to bind two. If it binds on the side you can bind multiple copies.
Erica Ollmann Saphire: So we haven’t — what we should have done and haven’t done is see how well it binds to a circular double-stranded RNA that has no end. We see what happens is it makes the cap first and then this backbone binder does the same interaction all the way down the rest. So if you keep polymerizing once it has this cap on there. Marburg virus doesn’t need the cap and it is happy to just polymerize. And so, another group has been doing similar structures and they see the same thing. Every time you crystallize an Ebola virus VP35 you have an end cap and every time you crystallize the Marburg VP5, you have a spiral. So based on that, I would say it is the backbone binder that might be dominant but we haven’t been able to really tease them apart yet.
You do lose binding when you have an overhang that projects into the space that needs to be occupied by the end cap. So, I don’t know what that says about relative infinity but it seems you need the end cap in order to get it going. The affinity is not high. Maybe 10 or maybe micromolar. So maybe you need some kind of affinity effect.
Male Audience: In the crystal structures of VP40, you showed a hexameric ring I didn’t see later. Is that involved in the cell during infection at any point?
Erica Ollmann Saphire: Hexamer versus octomer? We don’t know and we don’t even know if infected cells is even a complete ring or what it is — it’s the same interface 7but split open and spiraling around the nucleocapsid. We don’t know. We just know that you can get it to form both kinds of rings and one crystalized and the other didn’t.
Dr. Collins: We will now invite everybody to walk up the hall to the ribbon cutting. Before you do so, please join me in thanking Erica for a really fascinating seminar.