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BP: Fachverband Biologische Physik

BP 33: Biological Machines \& Motor Proteins

BP 33.6: Vortrag

Freitag, 18. März 2011, 12:00–12:15, ZEU 250

Actin filaments undergo local structural transitions at random sites — •Thomas Niedermayer¹, Antoine Jegou², Emmanuele Helfer², Guillaume Romet-Lemonne², Marie-France Carlier², and Reinhard Lipowsky¹ — ¹Abteilung Theorie und Bio-Systeme, Max-Planck-Institut für Kolloid- und Grenzflächenforschung, 14424 Potsdam, Germany — ²Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, 91198 Gif-sur-Yvette, France

After the polymerization of actin monomers into filaments, the actin-bound ATP is hydrolyzed into ADP, a process that is believed to decrease the filament stability. Recent experiments suggest the opposite behavior, however, namely that actin filaments become increasingly stable with time. Several mechanisms for this unexpected behavior have been proposed, ranging from structural transitions of the whole filament helix to pure artifacts arising, e.g., from the capping or surface attachment of the filament ends. We performed novel fluorescence microscopy experiments on single filaments to clarify this controversial issue. We find that filaments do indeed cease to depolymerize in an abrupt manner, and that this transition happens on relatively long time scales that exceed those of both ATP cleavage and phosphate release. We also developed a theory that allows us to distinguish the different possible transition mechanisms. A detailed comparison of theory and experiment implies that the sudden truncation of the shrinkage process does neither arise from artifacts nor from a collective transition of the whole filament. Instead, our results provide strong evidence for a local transition process occurring at random sites within the filament.