Cofilin is a pH sensor for actin free barbed end formation: role of phosphoinositide binding.
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.
Frantz
Christian
C
Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143, USA.
Barreiro
Gabriela
G
Dominguez
Laura
L
Chen
Xiaoming
X
Eddy
Robert
R
Condeelis
John
J
Kelly
Mark J S
MJ
Jacobson
Matthew P
MP
Barber
Diane L
DL
D008841:Actin Cytoskeleton / Q000737:chemistry / Q000378:metabolism*; D051339:Actin Depolymerizing Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D002465:Cell Movement; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008840:Microfilament Proteins / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D010716:Phosphatidylinositols / Q000378:metabolism*; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection
D051339:Actin Depolymerizing Factors; D000199:Actins; D008840:Microfilament Proteins; D010716:Phosphatidylinositols; D010982:Platelet-Derived Growth Factor; D015800:Protozoan Proteins; D017923:Sodium-Hydrogen Exchangers; C047604:actophorin protein, Acanthamoeba