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#G-actin

2 public questions tagged with this topic.

Cytoskeleton

Which actin-binding protein promotes actin polymerization by catalyzing the exchange of ADP for ATP on G-actin?

Actin nucleotide state dictates polymerization competence. ATP G actin incorporates into barbed end with high affinity Kd 0.1 micromolar, ADP G actin weak Kd 1 micromolar and depolymerizes. After filament turnover ADP actin accumulates needing recharge. Profilin, 15 kilodalton ubiquitous protein present at 50 to 100 micromolar, binds actin subdomain 1 and 3 cleft with 1 to 1 stoichiometry. Structural studies show binding opens nucleotide binding pocket between subdomains 2 and 4, reducing affinity for ADP 1000 fold and accelerating its dissociation rate from 0.02 to 1 per second, allowing abun

Ref: Pollard and Earnshaw, Cell Biology, Chapter 12: Profilin and Nucleotide Exchange on G-Actin.

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Cytoskeleton

What happens when the G-actin concentration is lower than Cc at both ends?

Filament mass reflects equilibrium between monomer pool and polymers determined by two Cc values. Plus end higher affinity due to ATP cap and hydrophobic pocket, minus end lower affinity bearing ADP actin. When total free G actin concentration falls below Cc for both ends, for instance after dilution into low ionic buffer, sequestration by thymosin beta4 or latrunculin A, or after activation of cofilin increasing off rate, association cannot compensate dissociation. Consequently subunits dissociate from both termini, filament shortens from both directions and ultimately disappears. This explai

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Actin Critical Concentration and Dynamics.

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