Impact of Profilin on Actin-Bound Nucleotide Exchange and Actin Polymerization Dynamics

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• 作者：Lynn A. Selden ; Henry J. Kinosian ; James E. Estes ; and Lewis C. Gershman
• 刊名：Biochemistry
• 出版年：1999
• 出版时间：March 2, 1999
• 年：1999
• 卷：38
• 期：9
• 页码：2769 - 2778
• 全文大小：117K
• 年卷期：v.38,no.9(March 2, 1999)
• ISSN：1520-4995

文摘

We have investigated the effects of profilin on nucleotide binding to actin and on steady stateactin polymerization. The rate constants for the dissociation of ATP and ADP from monomeric Mg-actin at physiological conditions are 0.003 and 0.009 s^-1, respectively. Profilin increases these dissociationrate constants to 0.08 s^-1 for MgATP-actin and 1.4 s^-1 for MgADP-actin. Thus, profilin can increasethe rate of exchange of actin-bound ADP for ATP by 140-fold. The affinity of profilin for monomericactin is found to be similar for MgATP-actin and MgADP-actin. Continuous sonication was used toallow study of solutions having sustained high filament end concentrations. During sonication at steadystate, F-actin depolymerizes toward the critical concentration of ADP-actin [Pantaloni, D., et al. (1984)J. Biol. Chem. 259, 6274-6283], our analysis indicates that under these conditions a significant numberof filaments contain terminal ADP-actin subunits. Addition of profilin to this system increases the polymerconcentration and increases the steady state ATPase activity during sonication. These data are explainedby the fast exchange of ATP for ADP on the profilin-ADP-actin complex, resulting in rapid ATP-actin regeneration. An important function of profilin may be to provide the growing ends of filamentswith ATP-actin during periods when the monomer cycling rate exceeds the intrinsic nucleotide exchangerate of monomeric actin.