Membrane remodelling events underpin basic cell processes such as transport of nutrients, growth and respiration. Molecular details behind different remodelling events are largely unknown and often subject to action of different curvature-inducing proteins (CIPs). Here, the involvement of CIPs in two types of membrane remodelling events; fission and fusion is under investigation.
Dynamin-like proteins perform membrane fission during the process of mitochondrial division. Currently, available structural data for dynamin-like proteins fail to sufficiently explain mechanistic details behind the fission event. All available crystal structures of dynamin homologs contain a self-assembly limiting mutation in the stalk region. Here, a crystal structure of a full-length eukaryotic dynamin-like protein (CmDnm1) in the native state is reported. The 7 Å structure uncovers a novel to eukaryotes hinge 1 closed conformation, which is also present in solution as shown by cysteine crosslinking and PET experiments. Moreover, a new tetrameric conformation of CmDnm1 in the off-membrane inactive state is visualised and validated by size exclusion chromatography, electron microscopy and protein crosslinking. In addition, negative-stain electron microscopy shows that CmDnm1 is able to remodel membranes by forming oligomeric rings that assembly into helical filaments. Based on the structural and biochemical data we propose a model for dynamin-like protein-driven membrane fission, in which dynamin is in the off-membrane novel tetrameric conformation, which self-assembles in the concentration dependent manner to form rings, which can then polymerase into long filaments and bend membranes.
Thylakoid membranes are maintained by an interplay of fission and fusion events. Recently, Vesicle inducing protein in plastids 1 (Vipp1) was shown to trigger membrane fusion in cyanobacteria and chloroplasts. As no high-resolution structural data for Vipp1 proteins presently exists, current descriptions of the mechanism of membrane fusion rely on ~ 20 Å models of Vipp1 oligomeric rings. Here we show a cryo-EM structure of Vipp1 rings with a side-to-side rather than top-to-bottom arrangement of monomers. We identified lipid binding domains as the outer- and inner-most projections of the ring. In addition, Vipp1 filaments were characterised in more detail, uncovering a helical assembly pattern. Based on our Vipp1 structures, updated models for membrane fusion and oligomeric assembly are proposed.