1521-0111/91/2/123–134$25.00 http://dx.doi.org/10.1124/mol.116.105064 MOLECULAR PHARMACOLOGY Mol Pharmacol 91:123–134, February 2017 Copyright ª 2017 by The American Society for Pharmacology and Experimental Therapeutics MINIREVIEW Dynamin Functions and Ligands: Classical Mechanisms Behind Mahaveer Singh, Hemant R. Jadhav, and Tanya Bhatt Department of Pharmacy, Birla Institute of Technology and Sciences Pilani, Pilani Campus, Rajasthan, India Received May 5, 2016; accepted November 17, 2016 Downloaded from ABSTRACT Dynamin is a GTPase that plays a vital role in clathrin-dependent pathophysiology of various disorders, such as Alzheimer’s disease, endocytosis and other vesicular trafficking processes by acting Parkinson’s disease, Huntington’s disease, Charcot-Marie-Tooth as a pair of molecular scissors for newly formed vesicles originating disease, heart failure, schizophrenia, epilepsy, cancer, dominant ’ from the plasma membrane. Dynamins and related proteins are optic atrophy, osteoporosis, and Down s syndrome. This review is molpharm.aspetjournals.org important components for the cleavage of clathrin-coated vesicles, an attempt to illustrate the dynamin-related mechanisms involved phagosomes, and mitochondria. These proteins help in organelle in the above-mentioned disorders and to help medicinal chemists division, viral resistance, and mitochondrial fusion/fission. Dys- to design novel dynamin ligands, which could be useful in the function and mutations in dynamin have been implicated in the treatment of dynamin-related disorders. Introduction GTP hydrolysis–dependent conformational change of GTPase dynamin assists in membrane fission, leading to the generation Dynamins were originally discovered in the brain and identi- of endocytic vesicles (Praefcke and McMahon, 2004; Ferguson at ASPET Journals on September 23, 2021 fied as microtubule binding partners. Dynamin is a 100-kDa and De Camilli, 2012). Dynamin has been correlated to the protein macromolecule, belonging to the superfamily of GTPases, pathophysiology of various disorders, such as Alzheimer’s which plays a major role in synaptic vesicle transport. Members disease (AD), Parkinson’s disease (PD), Huntington’sdisease of the dynamin family are found throughout the eukaryotic (HD), Charcot-Marie-Tooth disease (CMT), heart failure kingdom. The dynamin family includes dynamin 1 (DNM1), (HF), schizophrenia, epilepsy, cancer, optic atrophy, Down’s dynamin 2 (DNM2), and dynamin 3 (DNM3), which are known syndrome (DS), and osteoporosis. as classic dynamins. Each of these dynamins has the following five different domains: large N-terminal GTPase domain; mid- Domains of a Dynamin dle domain (MD); pleckstrin homology domain (PHD); GTPase effector domain (GED); and proline-rich domain (PRD) Dynamin and GTP together boost membrane fission by GTP (Heymann and Hinshaw 2009). hydrolysis and rapid displacement of dynamin from the Dynamins, other than classic dynamins, come under the membrane surface. The distinguishing architectural features category of dynamin-like proteins, which lacks PHD and PRD that are common to all dynamins and are distinct from other and assist in recruiting classic dynamins to cleave the vesicles. GTPases include the 300-amino acid large GTPase domain or It has been observed that membrane fission involves the the globular G-domain along with the presence of two activities of dynamins and GTP. GTPase-activating proteins additional domains: the MD and the GED. The globular facilitate hydrolysis of GTP into GDP with the help of GTPases, G-domain is composed of a central core that extends from a whereas guanine nucleotide exchange factors displace the six-stranded-b-sheet to an eight-stranded one by the addition generated GDP, thus favoring the next cycle of hydrolysis. The of 55 amino acids, and this domain is necessary for guanine nucleotide binding, resulting in hydrolysis (Reubold et al., dx.doi.org/10.1124/mol.116.105064. 2005). Two more characteristic sequences of the dynamin ABBREVIATIONS: Ab, amyloid-b; Ab, amyloid-b protein; AD, Alzheimer’s disease; ADBE, activity-dependent bulk endocytosis; APP, amyloid precursor protein; BACE-1, beta-site amyloid precursor protein cleaving enzyme 1; BSE, bundle signaling element; CCP, clathrin-coated pit; CME, clathrin-mediated endocytosis; CMT, Charcot-Marie-Tooth disease; CNM, centronuclear myopathy; DNM1, dynamin 1; DNM2, dynamin 2; DNM3, dynamin 3; Drp, dynamin-related protein; Drp1, dynamin-related protein 1; DS, Down’s syndrome; GED, GTPase effector domain; HD, Huntington’s disease; HF, heart failure; Htt, Huntington protein; LOAD, late-onset of Alzheimer disease; LRRK2, leucine-rich repeat kinase 2; LV, left ventricle; MD, middle domain; Mfn, mitofusin; mHtt, mutant Huntington protein; OPA1, mitochondrial dynamin-like GTPase; PCA, prostate cancer; PD, Parkinson’s disease; PDGFRa, platelet-derived growth factor receptor a; PHD, pleckstrin homology domain; PIP2, phosphatidylinositol-4-5- bisphosphate; PRD, proline-rich domain; RME, receptor-mediated endocytosis; SH3D, SRC homology 3 domain; SUMO, small ubiquitin-like modifier. 123 124 Singh et al. superfamily are MD and a C-terminal GED, which together vesicle membrane, the PHD orients toward the inner part of the constitute two distinct domains as stalk and bundle signaling helix, and polymerization drives membrane flow inside elements (BSEs). The BSE consists of three helices located on the helix, due to which the membrane gets constrained (50– the N and C terminus of GTPase domain and the C-terminus 20 nm) by dynamin coat. The elasticity of the membrane of the GED. The BSE conveys nucleotide-dependent confor- competes with the rigidity of the dynamin coat. The kinetics mational changes from the GTPase domain to the stalk and of dynamin fission depends on bending rigidity, tension, and control membrane activity in membrane fission. The stalk is constriction torque (Morlot et al., 2012). a combination of the MD and the amino-terminal portion of During polymerization, the force generated is responsible the GED. Depending on the information received from the for the deformation of the membrane, which can be measured BSE, the stalk mediates dimerization and tetramerization, with optical tweezers using a single-membrane tubule. An and results in the formation of rings and spirals (Wenger in vitro study indicates that dynamin is strong enough to curve et al., 2013). The MD and GED are linked by the PHD, which the membrane, and the late arrival of dynamin at the curvature is limited to classic dynamins and interacts directly with shows that it is recruited when the curvature starts forming. membrane bilayer (Klein et al., 1998; Ramachandran, 2011; Amphiphysin and endophilin are supposed to recruit dynamin Faelber et al., 2012). This domain is highly conserved and at the neck of clathrin-coated pits (CCPs). The assemblage of essential for dynamin functioning. It helps in binding to the dynamins at curvatures depends on various factors, such as Downloaded from negatively charged head group of phosphatidylinositol-4-5- negatively charged membranes, PIP2, the initial curvature of bisphosphate (PIP2), a membrane lipid that plays a role in the membrane, pH level, and salt concentration (Schmid and clathrin-mediated endocytosis (CME). Mutations in the MD Frolov, 2011). (R361S, R399A) or in the GED (I690K) in human DNM1 result in defective dimerization. Hydrolysis and Conformational Changes If these mutations occur in the stalk domain, they yield abnormally stable dynamin polymers that are resistant to The GTPase domain of dynamin, which is structurally similar molpharm.aspetjournals.org disassembly and disturb the process of GTP hydrolysis. The to the adenosine triphosphatase domain of kinesin, is responsi- PRD has a binding site for the SRC homology 3 domain (SH3D), ble for hydrolyzing GTP molecules through GTPase activity which is present in various dynamin-related proteins, such as (Song et al., 2004). A GTP binding motif known as switch-1 amphiphysin, endophilin, and synaptic dynamin binding pro- allows the GTPase domain to directly position itself in the tein (syndapin). Thus, amphiphysin, endophilin, and syndapin most favorable hydrolytic conformation, where positioning serve as binding partners of classic dynamins. The PRD is depends on interactions with other GTPase domains. Dyna- involved in an interaction with SH3D, and, thus, multiple min monomers do not work cooperatively, meaning that each dynamins are engaged in making a network with protein monomer burns its GTP independently. The conformational carrying SH3Ds. Various domains of dynamin are given in change associated with GTP hydrolysis has been partially at ASPET Journals on September 23, 2021 Fig. 1 (Urrutia et al., 1997; Ford et al., 2011). elucidated in the case of dynamin. GTP hydrolysis modulates the helical structure of dynamin, and constriction can reduce the radius of the membrane in its helix, which is opposed Mechanics of Fission: Assembly and by the elasticity of the membrane (Roux et al., 2006). Dynamin Polymerization generates rotational force during constriction, producing a conformational change that can be evaluated. The required Purified dynamin always assembles as a spiral structure, for one turn of dynamin to constrict a membrane tube from a supporting the hypothesis that dynamin wraps around the 10-nm radius (the radius of nonconstricted dynamin) to a 5-nm necks of nascent vesicles. Techniques, like gel filtration and radius (the constricted radius in the presence of GMP-PCP electron
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