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#capping protein

2 public questions tagged with this topic.

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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Cytoskeleton

Which protein caps the barbed (+) end of actin filaments, preventing further polymerization?

Length control at barbed end requires high affinity cappers preventing subunit addition. CapZ, known as capping protein CP alpha1 or alpha2 beta heterodimer, is major ubiquitous capper in mammals. Biochemical analysis shows binding Kd near 0.1 nanomolar, essentially irreversible without regulation. Crystal structure reveals mushroom shaped dimer where alpha subunit C terminal amphipathic helix binds hydrophobic pocket of ultimate actin subunit and beta subunit tentacle contacts penultimate subunit, sterically blocking monomer entry. In sarcomeres CapZ anchors thin filament plus end at Z disc l

Ref: Pollard and Earnshaw, Cell Biology, Chapter 12: Capping Proteins CapZ and Barbed End Regulation.

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