Actin filament assembly

Source: www.mechanobio.... (Mechanobiology Institute, Singapore). The actin network is made up of filamentous actin (F-actin). These filaments are highly dynamic in nature and comprise monomers of G-actin bound to either ATP (yellow) or ADP (blue). Assembly is powered by ATP hydrolysis and filament nucleation happens spontaneously in vitro. Polymerization: Addition of ATP-actin occurs at the barbed end, leading to filament elongation. Elongation will continue whilst the rate of elongation is greater than the loss of ADP-actin from the pointed end. Profilin preferentially binds to ATP-actin, inhibits nucleation and accelerates filament elongation in vivo. Depolymerization: When the dissociation rate of ADP-actin exceeds the rate of ATP-actin association, the filament shrinks. In vivo, this is aided by cofilin, which can severe filaments into short fragments and promote subunit loss from the pointed ends. Actin treadmilling occurs when the rate of association of ATP-actin and the rate of loss of ADP-actin are balanced.
Related links:
Filament Polarity: www.mechanobio....
Capping Protein: www.mechanobio....
Actin Nucleation: www.mechanobio....

[@toxikc4189]

People. Profilin inhibits nucleation and accelerates polymerization. These two are distinct

[@Mohammad-xe2qw]

What is the difference,Plz?

[@user-yp6me9by2b]

@@Mohammad-xe2qw Nucleation is the formation of a new filament while polymerization is the elongation of an existing filament. Profilin ensures monomers are not wasted on nucleation, but rather are directed towards making existing filaments longer.

[@ajhamton2616]

no audio?...i swear i checked my speakers..

[@rickykalendarov1176]

amazing video, explanation is so clear! I finally got it :)

[@Mechanobiology]

Hi, thanks for your comment.
Actin filaments are polarized. Monomers bind to the filament at the '-ve' end and hence filaments grow in one direction - that is from their 'barbed end'. This first requires the 'capping proteins' to be displaced from the end of the filament. If elongation factors like formin are involved, they also 'add' monomers to the same end.
You can read more on actin polarity, capping proteins & the critical concentration of G-actin in the links listed in the description

[@atishghosh10]

So cool

[@saragattola9614]

pls do more this is savage

[@tarakamaliasl9305]

Profilin proteins promote polymerization and growth, not inhibition. This is wrong.

[@chaztikov]

Is it possible that they promote polymerization of a stable actin filament, but prevent nucleation?

[@veeveebee2529]

I agree that it promotes polymerization. I learned that it only binds to Actin ADP, catalyses the exchange on ADP to ATP, which catalyzes polymerization.

[@tania38513]

i was confused about this after watching this video, Thank you very much

[@cilegnet]

Profilin alone inhibits the polimerisation of actin. But in the presence of formins for example, the polimerisation rate will be higher.

[@MsJoanaPaula]

Very nice video :) Made me understand the subject!

[@vithalbhaipatel1013]

Well show. Good information.

[@MrHumberto2205]

preferential addition of actin monomers to (+) end, not (-) end

[@vidhivora3578]

Amazing video

[@LikeaBosstoday]

quick question, when F-actin is in the steady-state and is treadmilling, are actin monomers still getting added to the -ve end? I know that there is net growth at the +ve end and net loss at the -ve end, but are there still some subunits being added at the -ve end?

[@DM-lt3zu]

I think yes.

[@tankmh4468]

yes

[@NeverSaySandwich1]

Is Bowfinger a good movie?

[@rubina4578]

Amazing😍

[@Eastvillage91]

Nice video, but it didn't show much about critical concentration... and can polymerisation only go in one direction and not the other way?

[@breetaylor9856]

old comment so not really a response to you, but responding to the question: polymerization occurs on both ends just as depolymerization also occurs on both ends. however, the important thing to remember is the rate at which it all occurs, if polymerization is happening faster than depolymerization, that end is going to grow; vice versa is depolymerization is happening faster than polymerization, the end is going to shrink. the barbed (+) end is growing and the pointed end (-) is shrinking, even though both polymerization and depolymerization is taking place on both ends (but again, just at different rates)
specifically for the question, polymerization can go in both directions, but growth is only taking place in one direction

[@kellysiemund6567]

Cheers!! I got it

[@sobster123]

some fuckin sound would be nice

[@fortazerty]

There's missing information ...

[@benjamincole9840]

Sick vid wanna collab?

[@aichamessous3783]

merci beaucoup

[@toxikc4189]

Tara they said nucleation😂

[@chlorophylle7892]

I find it so depressing xD

[@jannikheidemann3805]

This process keeps you alive.
What's depressing about that?

[@liamleeknow2012]

شآم مرت من هنا pre7🐞🍀✨

[@kevins8536]

What? This looks trippy but has nothing to do with real protein physics.
I think that that might just be someone's animation 'reel.'

[@584emad]

WRONG !!!!!!!! profilin promotes actin polymerisation and cofilin inhibits actin polymerisation