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Biophys. J. BioFAST: First Published August 5, 2005. doi:10.1529/biophysj.105.065383
© 2005 by the Biophysical Society.

A more recent version of this article appeared on November 1, 2005.
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CELL BIOPHYSICS

Morphology of the Lamellipodium and Organization of Actin Filaments at the Leading Edge of Crawling Cells

Erdinc Atilgan 1, Denis Wirtz 2 and Sean Sun 2*

1 Johns Hopkins Univ.
2 Johns Hopkins University

* To whom correspondence should be addressed. E-mail: ssun{at}jhu.edu.

Submitted on April 26, 2005
Revised on May 27, 2005
Accepted on 26 July 2005


  Abstract
Lamellipodium extension, incorporating actin filament dynamics and the cell membrane, is simulated in 3 dimensions. The actin filament network topology and the role of actin associated proteins such as Arp2/3 are examined. We find that the orientational pattern of the filaments is in accord with the experimental data only if the spatial orientation of the Arp2/3 complex is restricted during each branching event. We hypothesize that branching occurs when Arp2/3 is bound to WASP, which is in turn bound to Cdc42 signaling complex; Arp2/3 binding geometry is restricted by the membrane bound complex. Using mechanical and energetic arguments, we show that any membrane protein that is conical or trapezoidal in shape preferentially resides at the curved regions of the plasma membrane. We hypothesize that the transmembrane receptors involved in the recruitment of Cdc42/WASP complex has this property and concentrate at the leading edge. These features, combined with the mechanical properties of the cell membrane, explain why lamellipodium is a flat organelle.

Key Words: Actin Filament Network, Cell Motility, Computational Modeling, Lamellipodium, Membrane Proteins




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Copyright © 2005 by the Biophysical Society.