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Sep 26, 2021 18 tweets 5 min read Read on X
#Viral_Capsids

A look at viral capsids.
1/ The capsid is a strong protein structure that encloses and protects the viral genome. The most basic viruses will use a single protein produced many times to build the capsid. The more complex viruses will use multiple proteins to build their capsid structure.
2/ The basic structure of the viral capsid comes in 3 basic designs. They are Icosahedral, Helical and Complex.
3/ The Helical symmetry of capsids takes 1 protein and links them together into a very long string. That string is then wrapped into a helical structure like a tube.
4/ An example of a helical capsid virus is Ebola. This virus actually looks like a worm because of its helical capsid.
5/ The Icosahedral capsid is made up of triangles to form a sphere like shape. If you ever seen a 20 sided die from the D&D game, that is a perfect example of an icosahedral shape.
6/ The basic unit of the icosahedral capsid is a single viral protein often designated as Viral Protein 1 (VP1). Some viruses will use multiple proteins to form its basic triangle structure and will designate them VP1, VP2 and VP3.
7/ This small structure is the most basic building block of the icosahedral structure. When 3 of these proteins come together, they form the basic triangle of the icosahedral capsid. The single triangle is called a facet.
8/ The most basic virus is made up of only 20 facets. This is also called its T number. A T-1 virus would have 20 facets. A T-2 virus would have 40 facets and a T-3 virus would have 60 facets.
9/ Since each facet is made up of the 3 basic proteins, the T number that represents the facets gets multiplied by 3 to find out the total proteins in the capsid. For example a T-1 capsid has 20 facets with 3 proteins per facet = 60 total proteins.
10/ A T-3 capsid would have 20 x 3 facets or 60 total facets with 3 proteins to make up every facet. That would be 60 x 3 = 180 total proteins.
11/ When a capsid falls into icosahedral symmetry, it will have specific shapes if forms. There are 2 fold, 3 fold and 5 fold axes in each 20 facet capsid.
12/ As the virus capsid gets bigger into the T scale, the number of 5 fold axes increase so that the capsid goes from a basic of triangle faces to pentagon shaped faces made up of these 5 fold triangles shown below.
13/ In a large enough capsid, you will begin to see 6 fold axes of symmetry. They begin to look like the pattern on a soccer ball.
14/ The last Capsid is the Complex which is made up of both helical and icosahedral parts. The classic example of this type of virus is the bacteriophage.
15/ The head of the bacteriophage is made up of a basic icosahedral shape which is attached to a long tube that is made up of a helical structure. These do not harm humans and prey on bacteria hence their names.
16/ The Adeno Associated Virus (AAV) is a basic T-1 icosahedral capsid. Its made up of 20 facets. The most basic uses only 1 protein VP1 with 60 copies to make up the capsid. Others will use 3 different proteins with VP1, VP2 and VP3 in 20 copies of each to build the capsid.
17/ The AAV capsid is the smallest you can find. It only holds about 4,500 bases (4.5kb) of RNA or DNA genetic material.

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More from @Biotech2k1

May 30
🧵 $VKTX Profile:

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Intro to Management:
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Clinical Development:
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Regulatory Development:
They need expertise at navigating the regulatory process with the FDA. So far, they haven't had to deal much with the FDA. They are just starting phase 3. It will take some time before they get to that point. We will have to wait and see how it goes.

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Commercial Sales:
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VK2735:

Mechanism of Action:
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