Virology Lectures 2024 #4: Structure of viruses

Viral particles must not only protect the genome in its journey among hosts, but also come apart under the right conditions to release the genome into cells, a property called metastability. In this lecture we describe the two major forms of symmetry for building virus particles, helical and icosahedral. We discuss how to make small and large viruses, the triangulation number, quasiequivalence, and other components of virus particles such as spike glycoproteins and a lipid membrane.

[@WillNewcomb]

Mmm? Not sure if I'll listen. #2 & #3 were way beyond me! But I don't want to miss out on some gems!

[@climjames]

never let your lack of current understanding keep you from dipping in, lest ye never learn.

[@WillNewcomb]

@@climjames Perhaps I'll listen tonight! Thanks!

[@WillNewcomb]

Pretty pictures! That about sums up my comprehension of this lecture haha!!!

[@zhansayabauyrzhanova2492]

i did nt get this part: how pentamers in 60 subunit proteins made of only 5 subunits. pentamer 5x VP1, while T=8, 180 subunits 5x 3 = 15 subunits (VP1x5, VP2x5, VP3x5), right? if hexamer then, 18 subunits, right? can u elaborate on this, please?

[@paulgreen9059]

I kept thinking the icosahedrons could also be viewed as dodecahedrons since we were organizing the units into pentagons and slapping 12 of them together. It doesn't seem to work for large T values.

[@climjames]

20:00 the freezing method, I'm thinking they very slowly froze the virus and photographed the physical changes as it froze and from those snap shots they built a possible image. Am I close or far away? (Not a med student just interested.)

[@zhansayabauyrzhanova2492]

i did nt get this part: how pentamers in 60 subunit proteins made of only 5 subunits. pentamer 5x VP1, while T=3, 180 subunits 5x 3 = 15 subunits (VP1x5, VP2x5, VP3x5), right? if hexamer then, 18 subunits, right? can u elaborate on this, please?

[@mrkoba_05]

@@climjames cryo-EM needs very brief freezing for amorphous structure of samples.

[@zhansayabauyrzhanova2492]

51:00

[@zhansayabauyrzhanova2492]

i did nt get this part: how pentamers in 60 subunit proteins made of only 5 subunits. pentamer 5x VP1, while T=3, 180 subunits 5x 3 = 15 subunits (VP1x5, VP2x5, VP3x5), right? if hexamer then, 18 subunits, right? can u elaborate on this, please?

[@emmp8396]

If I'm understanding your question and the lecture correctly, you first need to remember that a subunit is just a single folded polypeptide chain. (06:06) Structural units are made up of at least 1 of these subunits. (29:48) The simplest Icosahedron is made of 20 triangles with each triangular face being made up of three of these identical protein subunits. 20 faces x 3 proteins per face = 60 coat protein subunits. The five subunits surrounding each vertex, or each point are arranged in a five‐fold symmetry. (42:50) In Professor's example at (51:00), he is showing a poliovirus in which the structural unit is 3 different subunit proteins, as opposed to one subunit protein example which was shown earlier at (43:35) Once this icosahedron gets larger, meaning with triangulation numbers >3, you simply can't build the correct structure using pentamers anymore and you have to use a combination of hexamers and pentamers. (46:10) As you do this, the binding energy between them changes a bit but they are still not covalently bound to each other. Hope this helps!