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The limits to (actin) growth

Guy’s Campus, London

19 Nov randall-bieling-2 Part of Randall Centre for Cell & Molecular Biophysics Seminar Series

The limits to (actin) growth

Speaker: Professor Peter Bieling, Max Planck Institute, Dortmund

Host: Matthias Krause

Abstract: Eukaryotic cells determine their external shape and internal organization through an actin cytoskeleton that forms a variety of networks. Common to all actin structures is their growth from soluble subunits that assemble into filaments. Past biochemical work has singled out the soluble actin concentration as the central factor controlling the filament growth speed. This, however, creates a conundrum: Soluble actin concentrations differ strongly between organisms, cell types and likely vary even across a single cell. Our current understanding of actin assembly suggests that these differences will result in dramatically different growth rates. How this would be compatible with the robust assembly of key cellular actin structures is unclear.

We developed new methods to visualize actin growth at physiological subunit concentrations for the first time. We discovered that under cell-like conditions, actin growth is remarkably insensitive to the concentration of free subunits. Instead, we identified a key reaction ­the release of the monomer-binding protein profilin from the filament end- as the bottleneck limiting the speed of growth. Interestingly, profilin release can be tuned by actin polymerases even at saturating profilin-actin concentrations. Our results uncovered an unexpected mechanism that changes our understanding of how actin filaments grow. This mechanism buffers the speed of actin growth against changes in the soluble subunit concentration, an essential requirement for the control of cellular actin dynamics.

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