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#actin nucleation

2 public questions tagged with this topic.

Cytoskeleton

What is the molecular weight of the Arp2/3 complex?

Arp2/3 complex purification and characterization resolved molecular composition and mass. Original isolation from Acanthamoeba by Pollard demonstrated seven polypeptides co fractionating through multiple chromatographic steps with actin binding activity. Subunit sequencing identified two actin related proteins Arp2 44 kilodalton and Arp3 50 kilodalton sharing actin fold, plus ARPC1 p40 WD repeat beta propeller 40 kilodalton, ARPC2 p34 34 kilodalton, ARPC3 p21 21 kilodalton, ARPC4 p20 20 kilodalton, ARPC5 p16 14 to 16 kilodalton. Sum calculated 224 kilodalton, sucrose gradient sedimentation and

Ref: Pollard and Earnshaw, Cell Biology, Chapter 12: Arp2/3 Complex Molecular Weight and Composition.

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Cytoskeleton

What is the role of FH2 domain in formin proteins?

Formin FH domains orchestrate assembly of long unbranched filaments in filopodia, dorsal stress fibers, yeast actin cables and contractile rings. FH2 domain 400 amino acids forms head to tail dimer with two actin binding sites, donut shaped ring encircling barbed end. Structural snapshots in different nucleotide states support stair stepping model where dimer steps onto newly added subunit without dissociating, remaining processively attached enabling continuous insertion while preventing CapZ binding. FH2 alone sufficient for nucleation in vitro, albeit slow, FH1 domain enhances efficiency. F

Ref: Pollard and Earnshaw, Cell Biology, Chapter 12: Formin FH2 Domain Nucleation and Processivity.

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