Cofilin is a pH sensor for actin free barbed end formation: role of phosphoinositide binding

• Published in: The Journal of cell biology Vol. 183; no. 5; pp. 865 - 879
• Main Authors: Frantz, Christian, Barreiro, Gabriela, Dominguez, Laura, Chen, Xiaoming, Eddy, Robert, Condeelis, John, Kelly, Mark J.S, Jacobson, Matthew P, Barber, Diane L
• Format: Journal Article
• Language: English
• Published: United States The Rockefeller University Press 01-12-2008; Rockefeller University Press
• Subjects: Actin Cytoskeleton - chemistry; Actin Cytoskeleton - metabolism; Actin depolymerizing factors; Actin Depolymerizing Factors - chemistry; Actin Depolymerizing Factors - genetics; Actin Depolymerizing Factors - metabolism; Actins; Actins - chemistry; Actins - metabolism; Animals; Binding Sites; Cell Line; Cell motility; Cell Movement; Cells; Cytoskeleton; Epithelial cells; Fibroblasts; Fibroblasts - metabolism; Humans; Hydrogen-Ion Concentration; Microfilament Proteins - metabolism; Microfilaments; Models, Molecular; Molecules; Mutation; NMR; Nuclear magnetic resonance; Nuclear Magnetic Resonance, Biomolecular; Phosphatidylinositols; Phosphatidylinositols - metabolism; Phosphorylation; Physiological regulation; Platelet-Derived Growth Factor - metabolism; Protein Conformation; Proteins; Protozoan Proteins - metabolism; Simulation; Sodium-Hydrogen Exchangers - genetics; Sodium-Hydrogen Exchangers - metabolism; Time Factors; Transfection
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200804161

Newly generated actin free barbed ends at the front of motile cells provide sites for actin filament assembly driving membrane protrusion. Growth factors induce a rapid biphasic increase in actin free barbed ends, and we found both phases absent in fibroblasts lacking H⁺ efflux by the Na-H exchanger NHE1. The first phase is restored by expression of mutant cofilin-H133A but not unphosphorylated cofilin-S3A. Constant pH molecular dynamics simulations and nuclear magnetic resonance (NMR) reveal pH-sensitive structural changes in the cofilin C-terminal filamentous actin binding site dependent on His133. However, cofilin-H133A retains pH-sensitive changes in NMR spectra and severing activity in vitro, which suggests that it has a more complex behavior in cells. Cofilin activity is inhibited by phosphoinositide binding, and we found that phosphoinositide binding is pH-dependent for wild-type cofilin, with decreased binding at a higher pH. In contrast, phosphoinositide binding by cofilin-H133A is attenuated and pH insensitive. These data suggest a molecular mechanism whereby cofilin acts as a pH sensor to mediate a pH-dependent actin filament dynamics.