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#actin dynamics

2 public questions tagged with this topic.

Cytoskeleton

The rapid turnover of actin filaments in vivo compared to in vitro is primarily due to:

Pure actin solution polymerized exhibits slow turnover due to low off rates 0.2 to 1 per second and minimal nucleation. In living cell turnover accelerated 50 to 100 fold evidenced by FRAP recovery half time 10 to 30 seconds for cortical actin. Acceleration attributed to collaborative action of cofilin and profilin. Cofilin severs ADP actin filaments increasing number of pointed ends depolymerizing at 10 per second vs 0.8 spontaneous and also increases off rate at pointed ends. Profilin ADP G actin complex undergoes rapid nucleotide exchange rate constant increase 1000 fold from 0.02 to 20 per

Ref: Pollard and Earnshaw, Cell Biology, Chapter 12: Rapid Actin Turnover by Cofilin Profilin In Vivo.

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Cytoskeleton

What is the function of CapZ in actin regulation?

Barbed end availability determines where new polymerization occurs in lamellipodia and filopodia. CapZ heterodimer alpha beta forms cap with extremely low dissociation rate half life 30 minutes in vitro. Binding interface extensive, burying 2000 square angstroms, alpha C terminal tentacle interacting with hydrophobic cleft between actin subdomains 1 and 3 of ultimate subunit, beta tentacle contacting penultimate subunit groove, physically blocking monomer docking. Quantitative fluorescence speckle microscopy shows most barbed ends in resting cells are capped, only about 5 percent free, but sec

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 18: CapZ Barbed End Capping Function.

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