Cell Biology

Putting the Squeeze On

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Science  06 Jun 2003:
Vol. 300, Issue 5625, pp. 1477-1479
DOI: 10.1126/science.300.5625.1477e

The protein actin generates powerful propulsive forces when it polymerizes into filaments in cell motility processes. In an effort to quantify the biophysical characteristics of these forces, Upadhyaya et al. and Giardini et al. have both used lipid vesicles coated with the bacterial actin-binding protein ActA, which is the molecule that enables the intracellular pathogen Listeria monocytogenes to harness actin for its own transport through the cytoplasm of the host cell. The polymerizing actin forms a cometlike tail behind the vesicles, which become deformed into teardrop shapes, round side in front, as they are pushed forward. The deformation provides an estimate of the compressive forces on the side of the vesicle and the retractive forces at the rear, which combine to produce a net propulsive force of a few nanonewtons on a vesicle 5 μm in diameter, or about 10 piconewtons per filament.—SMH

Proc. Natl. Acad. Sci. U.S.A. 100, 4521; 6493 (2003).

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