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Polymerization and mechanochemical action of dynamin
Orateur(s) :
Martin Lenz, Laboratoire de Physico-Chimie, Institut Curie, Paris
Salle :
C023 (RDC LR6 côté CECAM)
Quand :
28/01/2009 à 11:00
Sujet :
The protein dynamin and its analogues are believed to play a central role in most membrane fission event in eukaryotic cells. In close connexion with in vitro, cell-free quantitative experiments by Sandrine Morlot and Aurélien Roux in the group of Patricia Bassereau in Institut Curie, we seek to gain a theoretical understanding of its assembly on the one hand and of its mechanochemical (motor-like) action on the other hand.
Assembly
Dynamin polymerizes around membrane nanotubes pulled with optical tweezers from tension-controlled vesicles into long ( 10 µm) helical polymers. Experiments reveal the existence of a critical radius for polymerization as well as surprising facts about the nucleation and growth of the helix. From these we draw information about the assembly pathway and dynamin-membrane interactions. We also explore the relations between polymer nucleation and membrane fluctuations.
Mechanochemical action and fission
Using the energy from GTP hydrolysis, fully formed dynamin polymers twist, constrict and pull on the membrane, which results in its breaking. These changes of conformation can be monitored by attaching polystyrene beads to the polymer. We describe them by developing a generalized hydrodynamics formalism, which allows us to analyze the long length and time scale dynamics of the dynamin coat without making speculative assumptions about the unknown microscopic details of this process. Analyzing the mechanics of dynamin-coated tubes in this general framework, we find that
its dissipation is dominated by an effective (measurable) helix-membrane friction
GTP hydrolysis has rigorously the same effect as a force and torque
a controversy among biologists concerning the change of conformation of dynamin could be solved by a mechanical argument
the dynamin polymer is non-polar
experimentally observed supercoiling is accounted for by our model
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