Journal of Biological Chemistry
Volume 288, Issue 17, 26 April 2013, Pages 12102-12113
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Molecular Biophysics
Electrostatics Control Actin Filament Nucleation and Elongation Kinetics*

https://doi.org/10.1074/jbc.M113.456327Get rights and content
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The actin cytoskeleton is a central mediator of cellular morphogenesis, and rapid actin reorganization drives essential processes such as cell migration and cell division. Whereas several actin-binding proteins are known to be regulated by changes in intracellular pH, detailed information regarding the effect of pH on the actin dynamics itself is still lacking. Here, we combine bulk assays, total internal reflection fluorescence microscopy, fluorescence fluctuation spectroscopy techniques, and theory to comprehensively characterize the effect of pH on actin polymerization. We show that both nucleation and elongation are strongly enhanced at acidic pH, with a maximum close to the pI of actin. Monomer association rates are similarly affected by pH at both ends, although dissociation rates are differentially affected. This indicates that electrostatics control the diffusional encounter but not the dissociation rate, which is critical for the establishment of actin filament asymmetry. A generic model of protein-protein interaction, including electrostatics, explains the observed pH sensitivity as a consequence of charge repulsion. The observed pH effect on actin in vitro agrees with measurements of Listeria propulsion in pH-controlled cells. pH regulation should therefore be considered as a modulator of actin dynamics in a cellular environment.

Actin
Cytoskeleton
Fluorescence Correlation Spectroscopy
Microscopy
Sodium-Proton Exchange
Listeria
pH

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*

This work was supported, in whole or in part, by National Institutes of Health Grant GM58642. This work was also supported by Deutsche Forschungsgemeinschaft Grants SFB 863 and SPP 1464 and Emmy-Noether Programm (to J. D.), the Ludwig-Maximilians-Universität München (LMUInnovativBioImaging Network), the Nanosystems Initiative Munich, and the Max Planck Society.

This article contains supplemental Figs. S1–S3 and an additional reference.