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What does Thymosin do?
Thymosin sequesters away G-Actin by binding onto it (occupying it) so that it can't be added on to the + end of the Actin filament (the F-Actin) ==> thus, it inhibits polymerization by storing away G-Actin. And without accessible G-Actin, it's a bit hard to polymerize a F-Actin using them..!
What does Profilin do?
- Profilin attaches onto a ATP-bound G-Actin monomer unit and brings it over to the + end of the F-Acting, adding it on (with the ATP still intact) to the + end of the F-Actin. Thus, Profilin leads to polymerization of a microfilament (Actin).
What does Formin do?
Formin binds to the + end of F-Actin and encases the monomeric G-Actin at that location with its ring-like structure (like a hula-hoop around the + end). The presence of this Formin facilitates the addition of new ATP G-Actin units to the + end, leading to polymerization of the F-Actin in the + direction
What does ARP do?
ARP attaches onto and acts like a piece of Actin. When ARP is attached, because it looks just like polymerized G-Actins ("F-Actin"), non-polymerized G-Actins (aka 'Free Tubulin') are able to attach onto the ARP, thus giving rise to polymerization at a site that previously was incapable of polymerizing! Thus, ARP in a way "creates" a new binding site on a new "+" end.
What does Stathmin do?
- Stathmin attaches onto GDP-Tubulin and pops it off of the polymer Microtubule, whereafter it remains attached to the GDP-Tubulin, keeping it inactive and sequesters it away.
What can Stathmin bind onto?
Stathmin can ONLY bind onto GDP-Tubulin (and Stathmin can only do this when Stathmin itself is in its activated, non-Phosphorylated form - is like Stathmin is looking for a Phosphate so it can be happy and rest again)! This is why when Stathmin gets phosphorylated it releases the Tubulin, thus allowing the now-free Tubulin to be capable of getting phosphorylated and then attached back onto the + end of a Microtubule
Does Actin use ATP/ADP or GTP/GDP?
Does Tubulin use ATP/ADP or GTP/GDP?
Actin uses ATP/ADPs
Tubulin uses GTP/GDPs