Article

Conformational changes in Dnm1 support a contractile mechanism for mitochondrial fission

Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
Nature Structural & Molecular Biology (Impact Factor: 13.31). 01/2011; 18(1):20-6. DOI: 10.1038/nsmb.1949
Source: PubMed

ABSTRACT

Mitochondria are dynamic organelles that undergo cycles of fission and fusion. The yeast dynamin-related protein Dnm1 has been localized to sites of mitochondrial division. Using cryo-EM, we have determined the three-dimensional (3D) structure of Dnm1 in a GTP-bound state. The 3D map showed that Dnm1 adopted a unique helical assembly when compared with dynamin, which is involved in vesicle scission during endocytosis. Upon GTP hydrolysis, Dnm1 constricted liposomes and subsequently dissociated from the lipid bilayer. The magnitude of Dnm1 constriction was substantially larger than the decrease in diameter previously reported for dynamin. We postulate that the larger conformational change is mediated by a flexible Dnm1 structure that has limited interaction with the underlying bilayer. Our structural studies support the idea that Dnm1 has a mechanochemical role during mitochondrial division.

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    • "They have a defined shape and their size is comparable to the single lines. Indeed, these double structures, only detected in GFP-Bax WT images, resembled the spiral assemblies proposed for the dynamin-like protein Drp1 during mitochondrial fragmentation (Mears et al, 2011). To rule out potential effects due to the presence of endogenous Bax and Bak in the HeLa cells transfected with GFP-Bax, we also performed SMLM experiments in Bax/Bak double knockout HCT116 cells transfected with GFP-Bax. "
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    • "Using time-lapse electron microscopy (EM), we sought direct structural evidence for the observed Drp1-induced CL reorganization Volume 26 September 1, 2015 Cardiolipin in mitochondrial fission | 3113 interactions in Drp1 are considerably stronger on highly curved membranes than on relatively flat membranes, as for dynamin (Roux et al., 2010; Shlomovitz et al., 2011). Coupled with the lower GTPase activity observed for the tightly wound Drp1 polymer under the diffusion-restricted conditions on LTs, high membrane curvature likely serves to constrain the GTP-driven dynamics of the Drp1 polymer and/or the proposed treadmilling of the helical filament (Mears et al., 2011; Morlot et al., 2012; Shnyrova et al., 2013; Francy et al., 2015) in order to promote membrane fission. Moreover, recent studies suggest that conical lipids (here, CL and DOPE) in flat lipid bilayers induce packing defects similar to that induced by high positive membrane curvature upon sequestration (Vamparys et al., 2013). "
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    ABSTRACT: Cardiolipin (CL) is an atypical, dimeric phospholipid essential for mitochondrial dynamics in eukaryotic cells. Dynamin-related protein 1 (Drp1), a cytosolic member of the dynamin superfamily of large GTPases interacts with CL and functions to sustain the balance of mitochondrial division and fusion by catalyzing mitochondrial fission. Although recent studies have indicated a role for CL in stimulating Drp1 self-assembly and GTPase activity at the membrane surface, the mechanism by which CL functions in membrane fission, if at all, remains unclear. Here, using a variety of fluorescence spectroscopic and imaging approaches, together with model membranes, we demonstrate that Drp1 and CL function cooperatively in effecting membrane constriction toward fission in three distinct steps. These involve (i) the preferential association of Drp1 with CL localized at a high spatial density in the membrane bilayer, (ii) the reorganization of unconstrained, fluid-phase CL molecules in concert with Drp1 self-assembly, and (iii) the increased propensity of CL to transition from a lamellar, bilayer arrangement to an inverted hexagonal, nonbilayer configuration in the presence of Drp1 and GTP, resulting in the creation of localized membrane constrictions that are primed for fission. Thus, we propose Drp1 and CL function in concert to catalyze mitochondrial division. © 2015 by The American Society for Cell Biology.
    Full-text · Article · Jul 2015 · Molecular biology of the cell
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    • "Purified Drp1 is an X-shaped dimer that assembles into higher-order oligomers under a number of conditions, and it has the ability to tubulate anionic lipid membranes (Fröhlich et al., 2013; Ingerman et al., 2005; Koirala et al., 2013; Macdonald et al., 2014). GTP hydrolysis causes constriction of the tubulated membrane (Koirala et al., 2013; Mears et al., 2011). Drp1 accumulates at mitochondrial fission sites, and its constriction activity appears to be a driving force in fission (Fig. 1A). "
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    ABSTRACT: Mitochondrial dynamics, including fusion, fission and translocation, are crucial to cellular homeostasis, with roles in cellular polarity, stress response and apoptosis. Mitochondrial fission has received particular attention, owing to links with several neurodegenerative diseases. A central player in fission is the cytoplasmic dynamin-related GTPase Drp1, which oligomerizes at the fission site and hydrolyzes GTP to drive membrane ingression. Drp1 recruitment to the outer mitochondrial membrane (OMM) is a key regulatory event, which appears to require a pre-constriction step in which the endoplasmic reticulum (ER) and mitochondrion interact extensively, a process termed ERMD (ER-associated mitochondrial division). It is unclear how ER-mitochondrial contact generates the force required for pre-constriction or why pre-constriction leads to Drp1 recruitment. Recent results, however, show that ERMD might be an actin-based process in mammals that requires the ER-associated formin INF2 upstream of Drp1, and that myosin II and other actin-binding proteins might be involved. In this Commentary, we present a mechanistic model for mitochondrial fission in which actin and myosin contribute in two ways; firstly, by supplying the force for pre-constriction and secondly, by serving as a coincidence detector for Drp1 binding. In addition, we discuss the possibility that multiple fission mechanisms exist in mammals.
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