Purification, crystallization and preliminary X-ray crystallographic analysis of Arabidopsis thaliana dynamin-related protein 1A GTPase-GED fusion protein

Membrane fission by dynamin: what we know and what we need to know

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.

Structures of the yeast dynamin-like GTPase Sey1p provide insight into homotypic ER fusion

The crystal structures of the N-terminal cytosolic domain of Sey1p shed light on the mechanism of Sey1p-mediated ER membrane fusion.

Homotypic membrane fusion of the endoplasmic reticulum is mediated by dynamin-like guanosine triphosphatases (GTPases), which include atlastin (ATL) in metazoans and Sey1p in yeast. In this paper, we determined the crystal structures of the cytosolic domain of Sey1p derived from Candida albicans. The structures reveal a stalk-like, helical bundle domain following the GTPase, which represents a previously unidentified configuration of the dynamin superfamily. This domain is significantly longer than that of ATL and critical for fusion. Sey1p forms a side-by-side dimer in complex with GMP-PNP or GDP/AlF₄⁻ but is monomeric with GDP. Surprisingly, Sey1p could mediate fusion without GTP hydrolysis, even though fusion was much more efficient with GTP. Sey1p was able to replace ATL in mammalian cells, and the punctate localization of Sey1p was dependent on its GTPase activity. Despite the common function of fusogenic GTPases, our results reveal unique features of Sey1p.

Purification, crystallization and X-ray diffraction analysis of human dynamin-related protein 1 GTPase-GED fusion protein

The mechano-enzyme dynamin-related protein 1 plays an important role in mitochondrial fission and is implicated in cell physiology. Dysregulation of Drp1 is associated with abnormal mitochondrial dynamics and neuronal damage. Drp1 shares structural and functional similarities with dynamin 1 with respect to domain organization, ability to self-assemble into spiral-like oligomers and GTP-cycle-dependent membrane scission. Structural studies of human dynamin-1 have greatly improved the understanding of this prototypical member of the dynamin superfamily. However, high-resolution structural information for full-length human Drp1 covering the GTPase domain, the middle domain and the GTPase effector domain (GED) is still lacking. In order to obtain mechanistic insights into the catalytic activity, a nucleotide-free GTPase-GED fusion protein of human Drp1 was expressed, purified and crystallized. Initial X-ray diffraction experiments yielded data to 2.67 Å resolution. The hexagonal-shaped crystals belonged to space group P2(1)2(1)2, with unit-cell parameters a = 53.59, b = 151.65, c = 43.53 Å, one molecule per asymmetric unit and a solvent content of 42%. Expression of selenomethionine-labelled protein is currently in progress. Here, the expression, purification, crystallization and X-ray diffraction analysis of the Drp1 GTPase-GED fusion protein are presented, which form a basis for more detailed structural and biophysical analysis.