Question

What happens when MBL/Ficolin gets activated (i.e. binds ligand)? (what are the steps of lectin activation, 9)

Answer 1

When MBL/Ficolin gets activated and binds a ligand, it initiates the lectin activation pathway. This pathway involves the binding of MBL/Ficolin to the pathogen surface, activation of associated serine proteases, cleavage of C4 and C2 proteins, formation of C3 convertase, cleavage of C3 protein into C3a and C3b fragments, opsonization of the pathogen, formation of C5 convertase, and activation of C5 protein that triggers the downstream complement pathway and destruction of the pathogen.

Step-by-step explanation:

When MBL/Ficolin gets activated and binds a ligand, it initiates the lectin activation pathway. In this pathway, the ligand binding triggers a series of events:

1. The activated MBL/Ficolin binds to the pathogen surface.
2. This binding activates associated serine proteases, known as MASP-1, MASP-2, and MASP-3.
3. These proteases cleave C4 and C2 proteins, leading to the formation of C3 convertase.
4. Subsequently, C3 protein gets cleaved by the C3 convertase into C3a and C3b fragments.
5. C3b binds to the pathogen surface, promoting opsonization.
6. C3b also acts as the initiation point for the formation of C5 convertase, leading to the activation of C5 protein.
7. Activated C5 protein triggers the downstream complement pathway, forming the membrane-attack complex (MAC) and causing destruction of the pathogen.