The role of scaffold reshaping and disassembly in dynamin driven membrane fission.

Martina Pannuzzo,Markus Deserno,Zachary A Mcdargh

doi:10.7554/elife.39441

Abstract

The large GTPase dynamin catalyzes membrane fission in eukaryotic cells, but despite three decades of experimental work, competing and partially conflicting models persist regarding some of its most basic actions. Here we investigate the mechanical and functional consequences of dynamin scaffold shape changes and disassembly with the help of a geometrically and elastically realistic simulation model of helical dynamin-membrane complexes. Beyond changes of radius and pitch, we emphasize the crucial role of a third functional motion: an effective rotation of the filament around its longitudinal axis, which reflects alternate tilting of dynamin's PH binding domains and creates a membrane torque. We also show that helix elongation impedes fission, hemifission is reached via a small transient pore, and coat disassembly assists fission. Our results have several testable structural consequences and help to reconcile mutual conflicting aspects between the two main present models of dynamin fission-the two-stage and the constrictase model.

Highlights

Of the three 80% homologous mammalian isoforms of dynamin, Dyn1, highly expressed in neurons, has been studied best (Hinshaw, 2000; Praefcke and McMahon, 2004)
Crystallographic analysis (Chen et al, 2004; Faelber et al, 2011; Ferguson et al, 1994; Ford et al, 2011; Zhang and Hinshaw, 2001; Chappie et al, 2010) reveals five distinct domains: an N-terminal GTPase or G-domain; a ‘stalk’ region consisting of a four helix bundle; the signaling bundle signaling element (BSE) domain that links G-domain and stalk; a pleckstrin homology (PH) domain binding phosphatidylinositol-4,5-biphosphate (PIP2) lipids; and a proline-rich C-terminal domain (PRD) that mediates interactions with membrane scaffolding proteins
Since K44ADyn1 is very inefficient in GTP hydrolysis, which is necessary for remodeling (Zhang and Hinshaw, 2001; Chappie et al, 2011), this mutant is believed to trap the system in a pre-fission state

Summary

Introduction

Of the three 80% homologous mammalian isoforms of dynamin, Dyn, highly expressed in neurons, has been studied best (Hinshaw, 2000; Praefcke and McMahon, 2004). Dynamin monomers oligomerize via their stalks in a criss-cross fashion, resulting in stable dimers (Cocucci et al, 2014) or tetramers (Ramachandran et al, 2007) in solution Continuing this assembly path yields helical filaments (Carr and Hinshaw, 1997), which have an outer diameter of about 50 nm and a helical pitch (i.e., height increment during one complete helical turn) between 10 nm and 20 nm in the absence of GTP (Chen et al, 2004). Since K44ADyn is very inefficient in GTP hydrolysis, which is necessary for remodeling (Zhang and Hinshaw, 2001; Chappie et al, 2011), this mutant is believed to trap the system in a pre-fission state. This leaves open the role of GTP activity, with presently two major competing scenarios: the two-stage and the constrictase model

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