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Membrane contact sites (MCS) facilitate communication between organelles. Casler et al. (https://doi.org/10.1083/jcb.202308144) show that tripartite MCS between mitochondria, the endoplasmic reticulum (ER), and the plasma membrane (PM) regulate mitochondrial division and the distribution of phosphatidylinositol 4-phosphate [PI(4)P] on the PM. [ABSTRACT FROM AUTHOR]

The mechanochemical 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 human dynamin tetramer in the nucleotide-free state. Combining structural data with mutational studies, oligomerization measurements and Markov state models of molecular dynamics simulations, we suggest a mechanism by which oligomerization of dynamin is linked to the release of intramolecular autoinhibitory interactions. We elucidate how mutations that interfere with tetramer formation and autoinhibition can lead to the congenital muscle disorders Charcot-Marie-Tooth neuropathy (4) and centronuclear myopathy (5), respectively. Notably, 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 signalling element [...]

Phosphoinositides serve crucial roles in cell physiology, ranging from cell signalling to membrane traffic (1,2). Among the seven eukaryotic phosphoinositides the best studied species is phosphatidylinositol-4,5-bisphosphate (PI(4,5)[P.sub.2]), which is concentrated at the plasma membrane where, among other functions, it is required for the nucleation of endocytic clathrin-coated pits (3-6). No phosphatidylinositol other than PI(4,5)[P.sub.2] has been implicated in clathrin-mediated endocytosis, whereas the subsequent endosomal stages of the endocytic pathway are dominated by phosphatidylinositol 3-phosphates(PI(3)P) (7). How phosphatidylinositol conversion from PI(4,5)[P.sub.2]-positive endocytic intermediates to PI(3)P-containing endosomes is achieved is unclear. Here we show that formation of phosphatidylinositol-3,4-bisphosphate (PI(3,4)[P.sub.2]) by class II phosphatidylinositol-3-kinase C2α (PI(3)K C2α) spatiotemporally controls clathrin-mediated endocytosis. Depletion of PI(3,4)[P.sub.2] or PI(3)K C2α impairs the maturation of late-stage clathrin-coated pits before fission. Timed formation of PI(3,4)[P.sub.2] by PI(3)K C2α is required for selective enrichment of the BAR domain protein SNX9 at late-stage endocytic intermediates. These findings provide a mechanistic framework for the role of PI(3,4)[P.sub.2] in endocytosis and unravel a novel discrete function of PI(3,4)[P.sub.2] in a central cell physiological process., PI(4,5)[P.sub.2] generation by phosphatidylinositol phosphate-5-kinases (phosphatidylinositol-5-kinases) is required for recruitment of early PI(4,5)[P.sub.2]-associated coat components to mediate clathrin-coated pit (CCP) nucleation in clathrin-mediated endocytosis (CME) (1,5). Although phosphatidylinositol-5-kinases can associate [...]

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., Dynamin, the founding member of the dynamin superfamily, is a 100-kDa mechanochemical enzyme (Fig. 1a) involved in the scission of clathrin-coated vesicles from the plasma membrane (1). The brain-specific isoform [...]

Proteins of the dynamin superfamily are mechanochemical GTPases, which mediate nucleotide-dependent membrane remodeling events. The founding member dynamin is recruited to the neck of clathrin-coated endocytic vesicles where it oligomerizes into helical filaments. Nucleotide-hydrolysis-induced conformational changes in the oligomer catalyze scission of the vesicle neck. Here, we review recent insights into structure, function, and oligomerization of dynamin superfamily proteins and their roles in human diseases. We describe in detail the molecular mechanisms how dynamin oligomerizes at membranes and introduce a model how oligomerization is linked to membrane fission. Finally, we discuss molecular mechanisms how mutations in dynamin could lead to the congenital diseases, Centronuclear Myopathy and Charcot-Marie Tooth disease., (Copyright © 2013 Elsevier Inc. All rights reserved.)