INF2-mediated severing through actin filament encirclement and disruption.

Abstract

BACKGROUND:

INF2 is a formin protein with the unique ability to accelerate both actin polymerization and depolymerization, the latter requiring filament severing. Mutations in INF2 lead to the kidney disease focal segmental glomerulosclerosis (FSGS) and the neurological disorder Charcot-Marie Tooth disease (CMTD).

RESULTS:

Here, we compare the severing mechanism of INF2 with that of the well-studied severing protein cofilin. INF2, like cofilin, binds stoichiometrically to filament sides and severs in a manner that requires phosphate release from the filament. In contrast to cofilin, however, INF2 binds ADP and ADP-Pi filaments equally well. Furthermore, two-color total internal reflection fluorescence (TIRF) microscopy reveals that a low number of INF2 molecules, as few as a single INF2 dimer, are capable of severing, while measurable cofilin-mediated severing requires more extensive binding. Hence, INF2 is a more potent severing protein than cofilin. While a construct containing the FH1 and FH2 domains alone has some severing activity, addition of the C-terminal region increases severing potency by 40-fold, and we show that the WH2-resembling DAD motif is responsible for this increase. Helical 3D reconstruction from electron micrographs at 20 Å resolution provides a structure of filament-bound INF2, showing that the FH2 domain encircles the filament.

CONCLUSIONS:

We propose a severing model in which FH2 binding and phosphate release causes local filament deformation, allowing the DAD to bind adjacent actin protomers, further disrupting filament structure.

• Authors: Pinar S Gurel, Peng Ge, Elena E Grintsevich, Rui Shu, Laurent Blanchoin, Z Hong Zhou, Emil Reisler, Henry N Higgs
• Journal: Current biology : CB (Curr Biol) Vol. 24 Issue 2 Pg. 156-164 (Jan 20 2014) ISSN: 1879-0445 [Electronic] England
• PMID: 24412206 (Publication Type: Journal Article, Research Support, American Recovery and Reinvestment Act, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.

Chemical References

• Microfilament Proteins

Topics

• Actin Cytoskeleton (metabolism, ultrastructure)
• Animals
• Microfilament Proteins (chemistry, metabolism)
• Microscopy, Electron
• Models, Molecular
• Protein Binding
• Protein Structure, Quaternary
• Protein Structure, Tertiary
• Rabbits