Immune System

Our Immune System is what keeping us safe when they can. It is true that the system requires several cells, but proteins also play a vital role in this system.

 

The Complement System

A weapon of 30+ types of proteins, guided by chemistry only is able to defense us from some of the pathogens.

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How it works ?

Step 1 : C3 activation and crippling

The activation of C3 proteins are quite complicated and therefore this article leaves this to the internet. Once a C3 protein has been activated, it splits itself into 2 parts : C3a and C3b.

C3a proteins can attract passive immune cells like phagocytes to phagocytosis the phatogens.

C3b proteins only have a fraction of a second to seek any pathogens and attach themselves onto the pathogens else they will be neutralize by water molecules. After attaching, C3b will change its shape, causing it able to combine with other proteins like so (PS : the fomular below may not be in accurate format):

C3b + B -> C3bB -(D)-> C3bBb + Ba

C3bBb + P -> C3bBbP (this protein can activate C3 proteins and therefore it is called as a "C3 Convertase")

C3b proteins which attached to pathogens also make phagocytosis easier.

Step 2 : Drilling

when a C3b protein is combined with a C3 Convertase, this whole structure is a C5 convertase, activating C5 proteins and breaking them into 2 parts : C5a and C5b. C5b can be combined with C6, C7 and C8 proteins and a Membrane Attack Complex (MAC) is then made, long proteins can be anchored through the membrane of the pathogen with MAC, just like poking a hole, letting the inside of the pathogen flowing outside and the job is done.

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Kurzgesagt done an amazing job on explaining the Complement System, this article is written based on their video: https://www.youtube.com/watch?v=BSypUV6QUNw