Dynamin is a mechanochemical GTPase that oligomerizes around the neck of clathrin-coated pits and catalyses vesicle scission in a GTP-hydrolysis-dependent manner. The molecular details of oligomerization and the mechanism of the mechanochemical coupling are currently unknown. Here we present the crystal structure of human dynamin 1 in the nucleotide-free state with a four-domain architecture comprising the GTPase domain, the bundle signalling element, the stalk and the pleckstrin homology domain. Dynamin 1 oligomerized in the crystals via the stalks, which assemble in a criss-cross fashion. The stalks further interact via conserved surfaces with the pleckstrin homology domain and the bundle signalling element of the neighbouring dynamin molecule. This intricate domain interaction rationalizes a number of disease-related mutations in dynamin 2 and suggests a structural model for the mechanochemical coupling that reconciles previous models of dynamin function.

The large GTPase dynamin is the first protein shown to catalyze membrane fission. Dynamin and its related proteins are essential to many cell functions, from endocytosis to organelle division and fusion, and it plays a critical role in many physiological functions such as synaptic transmission and muscle contraction. Research of the past three decades has focused on understanding how dynamin works. In this review, we present the basis for an emerging consensus on how dynamin functions. Three properties of dynamin are strongly supported by experimental data: first, dynamin oligomerizes into a helical polymer; second, dynamin oligomer constricts in the presence of GTP; and third, dynamin catalyzes membrane fission upon GTP hydrolysis. We present the two current models for fission, essentially diverging in how GTP energy is spent. We further discuss how future research might solve the remaining open questions presently under discussion.

Dynamin 1-like protein (DNM1L) mediates fission of mitochondria and peroxisomes, and dysfunction of DNM1L has been implicated in several neurological disorders. To study the molecular basis of mitochondrial remodelling, we determined the crystal structure of DNM1L that is comprised of a G domain, a bundle signalling element and a stalk. DNM1L assembled via a central stalk interface, and mutations in this interface disrupted dimerization and interfered with membrane binding and mitochondrial targeting. Two sequence stretches at the tip of the stalk were shown to be required for ordered assembly of DNM1L on membranes and its function in mitochondrial fission. In the crystals, DNM1L dimers further assembled via a second, previously undescribed, stalk interface to form a linear filament. Mutations in this interface interfered with liposome tubulation and mitochondrial remodelling. Based on these results and electron microscopy reconstructions, we propose an oligomerization mode for DNM1L which differs from that of dynamin and might be adapted to the remodelling of mitochondria.

Human myxovirus resistance protein 1 (MxA) is an interferon-induced dynamin-like GTPase that acts as a cell-autonomous host restriction factor against many viral pathogens including influenza viruses. To study the molecular principles of its antiviral activity, we determined the crystal structure of nucleotide-free MxA, which showed an extended three-domain architecture. The central bundle signaling element (BSE) connected the amino-terminal GTPase domain with the stalk via two hinge regions. MxA oligomerized in the crystal via the stalk and the BSE, which in turn interacted with the stalk of the neighboring monomer. We demonstrated that the intra- and intermolecular domain interplay between the BSE and stalk was essential for oligomerization and the antiviral function of MxA. Based on these results, we propose a structural model for the mechano-chemical coupling in ring-like MxA oligomers as the principle mechanism for this unique antiviral effector protein.

The mechano-chemical protein dynamin is the prototype of the dynamin superfamily of large GTPases, which shape and remodel membranes in diverse cellular processes 1 .Dynamin forms predominantly tetramers in the cytosol, which oligomerize at the neck of clathrin-coated vesicles to mediate constriction and subsequent scission of the membrane 1 . Previous studies have described the architecture of dynamin dimers 2,3 , but the molecular determinants for dynamin assembly and its regulation have remained unclear. Here, we present the crystal structure of the nucleotide-free dynamin tetramer.Combining structural data with mutational studies, oligomerization measurements and molecular dynamics simulations, we suggest a mechanism of how oligomerization of dynamin is linked to the release of intramolecular auto-inhibitory interactions. We elucidate how mutations that interfere with tetramer formation and auto-inhibition can lead to the congenital diseases Charcot-Marie-Tooth neuropathy (CMT) 4 and centronuclear myopathy (CNM) 5 , respectively. Strikingly, the bent shape of the tetramer explains how dynamin assembles into a right-handed helical oligomer of defined diameter, which has direct implications for its function in membrane constriction.The three highly conserved vertebrate isoforms of dynamin contain five distinct domains (Extended Data Fig. 1a): an N-terminal GTPase (G) domain mediating nucleotide binding and hydrolysis, a bundle signaling element (BSE), a stalk, a pleckstrin homology (PH) domain involved in lipid binding, and a proline rich domain (PRD) mediating interaction with BAR-and SH3-domain containing scaffolding proteins 6 . To exert its function in clathrinmediated endocytosis (CME), dynamin assembles via the stalks into a helical array surrounding the necks of invaginating clathrin-coated pits (CCP) 7,8 . Dimerization of GTPbound G domains from neighboring helical rungs induces GTP hydrolysis 9 . The ensuing conformational changes are thought to be transmitted from the G domain via the BSE to the stalk resulting in a sliding motion of adjacent helix rungs, concomitant helix constriction 10 , and eventually membrane scission. The inherent tendency to form large assemblies at high protein concentrations has hampered crystallization of dynamin in the past. The use of non-3 oligomerizing mutants led to crystal structures of dynamin 1 2,3 . However, the postulated higher-order assembly interface was not resolved in these structures leaving the oligomerization mechanism unaddressed.We reasoned that an alternative assembly-affecting mutation, such as K361S in dynamin 3 11 , may disturb the oligomerization interface to a lesser extent than the previously used mutants. We obtained crystals of nucleotide-free dynamin 3-K361S lacking the PRD (dynamin 3(∆PRD)-K361S) that diffracted to 3.7 Å (Methods, Extended Data Fig. 1, Extended Data Table 1). Indeed, the asymmetric unit of the crystal lattice contained a dynamin tetramer that did not form the filamentous superstructures seen for dynamin 1 2,3 .The dynamin tetr...