title: A direct-transfer polymerization model explains how the multiple profilin-binding sites in the actoclampin motor promote rapid actin-based motility.
abstract: The high actin-based motility rates observed in nonmuscle cells require the per-second addition of 400-500 monomers to the barbed ends of growing actin filaments. The chief polymerization-competent species is profilin.actin.ATP (present at 5-40 microM intracellular concentrations), whereas G-actin.ATP is much less abundant ( approximately 0.1-1 microM). While earlier studies unambiguously demonstrated that profilin.actin is highly concentrated within the polymerization zone, profilin-actin localization on the motile surface cannot increase the local solution-phase concentration of polymerizable actin. To explain these high rates of actin polymerization, we present and analyze a novel polymerization model in which monomers are directly transferred to growing filament ends in the actoclampin motor. This direct-transfer polymerization mechanism endows the polymerization zone with properties unavailable to bulk-phase actin monomers, and our model also indicates why profilin is the ideal mobile carrier for actin monomers.
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D003285:Contractile Proteins; D007700:Kinetics; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D008962:Models, Theoretical; D009068:Movement / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011108:Polymers; D051304:Profilins; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012760:Shigella / Q000502:physiology
chemical_list: D000199:Actins; D003285:Contractile Proteins; D008840:Microfilament Proteins; D011108:Polymers; D051304:Profilins; D011994:Recombinant Proteins