Quantitative Analysis of Membrane Deformation and Fission Induced by Dynamin GTPase Activity

Abstract

Dynamin is widely used by cells to sever lipid bilayers. During this process a short helical dynamin polymer (1 to 3 helical turns) assembles around a membrane tubule and reduces its radius and pitch upon GTP hydrolysis. This deformation is thought to be crucial for dynamin's severing action and results in an observable twisting of the helix [1]. Here we quantitatively study the factors determining the dynamics of this deformation by studying long dynamin. We perform in vitro experiments where we attach small beads to the dynamin helix and track their rotation in real time, thus collecting information about the space and time dependence of the deformation. Longer helices deform more slowly as predicted by a generalized hydrodynamics theoretical model [2]. Further agreement between experiments and theory indicates that the concerted deformation dynamics is dominated by the draining of the membrane out of the helix, allowing us to quantitatively characterize helix-membrane interactions [3]. We also study the dynamics of tube fission induced by dynamin GTPase activity. Membrane nanotubes are pulled from Giant Unilamellar Vesicles (GUV) using optical tweezers and membrane tension is set by aspirating the GUVs within a micropipette. Dynamin and GTP are injected near the tube. Tubes always break few seconds after dynamin starts polymerizing around the tube. We show that probability of fission depends on GTP concentration, no global depolymerization occurs during GTP hydrolysis and membrane geometry affects fission.[1] Aurelien Roux, Katherine Uyhazi, Adam Frost, and Pietro De Camilli. Nature 2006.[2] Martin Lenz, Jacques Prost, and Jean-Francois Joanny. Phys. Rev. E 2008.[3] Sandrine Morlot, Martin Lenz, Jacques Prost, Jean-Francois Joanny, Aurelien Roux. submitted