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Vann Bennett - One of the best experts on this subject based on the ideXlab platform.
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an adaptable spectrin ankyrin based mechanism for long range organization of plasma membranes in vertebrate tissues
Current Topics in Membranes, 2016Co-Authors: Vann Bennett, Damaris N. LorenzoAbstract:Ankyrins are membrane-associated proteins that together with their spectrin partners are responsible for micron-scale organization of vertebrate plasma membranes, including those of erythrocytes, excitable membranes of neurons and heart, lateral membrane domains of columnar epithelial cells, and striated muscle. Ankyrins coordinate functionally related membrane transporters and cell adhesion proteins (15 protein families identified so far) within plasma membrane compartments through independently evolved interactions of intrinsically disordered sequences with a highly conserved peptide-binding groove formed by the ANK repeat solenoid. Ankyrins are coupled to spectrins, which are elongated organelle-sized proteins that form mechanically resilient arrays through cross-linking by specialized actin filaments. In addition to protein interactions, cellular targeting and assembly of spectrin/ankyrin domains also critically depend on palmitoylation of ankyrin-G by aspartate-histidine-histidine-cysteine 5/8 palmitoyltransferases, as well as interaction of beta-2 spectrin with phosphoinositide lipids. These lipid-dependent spectrin/ankyrin domains are not static but are locally dynamic and determine membrane identity through opposing endocytosis of bulk lipids as well as specific proteins. A partnership between spectrin, ankyrin, and cell adhesion molecules first emerged in bilaterians over 500 million years ago. Ankyrin and spectrin may have been recruited to plasma membranes from more ancient roles in organelle transport. The basic bilaterian spectrin-ankyrin toolkit markedly expanded in vertebrates through gene duplications combined with variation in unstructured intramolecular regulatory sequences as well as independent evolution of ankyrin-binding activity by ion transporters involved in action potentials and calcium homeostasis. In addition, giant vertebrate Ankyrins with specialized roles in axons acquired new coding sequences by exon shuffling. We speculate that early axon initial segments and epithelial lateral membranes initially were based on spectrin-ankyrin-cell adhesion molecule assemblies and subsequently served as "incubators," where ion transporters independently acquired ankyrin-binding activity through positive selection.
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giant ankyrin g stabilizes somatodendritic gabaergic synapses through opposing endocytosis of gabaa receptors
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Wei Chou Tseng, Paul M Jenkins, Masashi Tanaka, Richard Mooney, Vann BennettAbstract:GABAA-receptor-based interneuron circuitry is essential for higher order function of the human nervous system and is implicated in schizophrenia, depression, anxiety disorders, and autism. Here we demonstrate that giant ankyrin-G (480-kDa ankyrin-G) promotes stability of somatodendritic GABAergic synapses in vitro and in vivo. Moreover, giant ankyrin-G forms developmentally regulated and cell-type-specific micron-scale domains within extrasynaptic somatodendritic plasma membranes of pyramidal neurons. We further find that giant ankyrin-G promotes GABAergic synapse stability through opposing endocytosis of GABAA receptors, and requires a newly described interaction with GABARAP, a GABAA receptor-associated protein. We thus present a new mechanism for stabilization of GABAergic interneuron synapses and micron-scale organization of extrasynaptic membrane that provides a rationale for studies linking ankyrin-G genetic variation with psychiatric disease and abnormal neurodevelopment.
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a hierarchy of ankyrin spectrin complexes clusters sodium channels at nodes of ranvier
Nature Neuroscience, 2014Co-Authors: Daniel R. Zollinger, Kaejiun Chang, Michael C Stankewich, Vann Bennett, Edward C. Cooper, Matthew N RasbandAbstract:The scaffolding protein ankyrin-G is required for Na(+) channel clustering at axon initial segments. It is also considered essential for Na(+) channel clustering at nodes of Ranvier to facilitate fast and efficient action potential propagation. However, notwithstanding these widely accepted roles, we show here that ankyrin-G is dispensable for nodal Na(+) channel clustering in vivo. Unexpectedly, in the absence of ankyrin-G, erythrocyte ankyrin (ankyrin-R) and its binding partner βI spectrin substitute for and rescue nodal Na(+) channel clustering. In addition, channel clustering is also rescued after loss of nodal βIV spectrin by βI spectrin and ankyrin-R. In mice lacking both ankyrin-G and ankyrin-R, Na(+) channels fail to cluster at nodes. Thus, ankyrin R-βI spectrin protein complexes function as secondary reserve Na(+) channel clustering machinery, and two independent ankyrin-spectrin protein complexes exist in myelinated axons to cluster Na(+) channels at nodes of Ranvier.
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a hierarchy of ankyrin spectrin complexes clusters sodium channels at nodes of ranvier
Nature Neuroscience, 2014Co-Authors: Daniel R. Zollinger, Kaejiun Chang, Michael C Stankewich, Vann Bennett, Edward C. Cooper, Matthew N RasbandAbstract:Previous work has suggested that the scaffolding protein ankyrin G is essential for the clustering of Na+ channels at the nodes of Ranvier. However, in this study, the authors show that, in the absence of ankyrin G, the complex of ankyrin R and βI spectrin can mediate Na+ channel clustering at the nodes.
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ankyrin g palmitoylation and βii spectrin binding to phosphoinositide lipids drive lateral membrane assembly
Journal of Cell Biology, 2014Co-Authors: Khadar Abdi, Vann BennettAbstract:Ankyrin-G and βII-spectrin colocalize at sites of cell–cell contact in columnar epithelial cells and promote lateral membrane assembly. This study identifies two critical inputs from lipids that together provide a rationale for how ankyrin-G and βII-spectrin selectively localize to Madin-Darby canine kidney (MDCK) cell lateral membranes. We identify aspartate-histidine-histidine-cysteine 5/8 (DHHC5/8) as ankyrin-G palmitoyltransferases required for ankyrin-G lateral membrane localization and for assembly of lateral membranes. We also find that βII-spectrin functions as a coincidence detector that requires recognition of both ankyrin-G and phosphoinositide lipids for its lateral membrane localization. DHHC5/8 and βII-spectrin colocalize with ankyrin-G in micrometer-scale subdomains within the lateral membrane that are likely sites for palmitoylation of ankyrin-G. Loss of either DHHC5/8 or ankyrin-G–βII-spectrin interaction or βII-spectrin–phosphoinositide recognition through its pleckstrin homology domain all result in failure to build the lateral membrane. In summary, we identify a functional network connecting palmitoyltransferases DHHC5/8 with ankyrin-G, ankyrin-G with βII-spectrin, and βII-spectrin with phosphoinositides that is required for the columnar morphology of MDCK epithelial cells.
Stephen Lambert - One of the best experts on this subject based on the ideXlab platform.
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nav1 5 e1053k mutation causing brugada syndrome blocks binding to ankyrin g and expression of nav1 5 on the surface of cardiomyocytes
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: Ilaria Rivolta, Stephen Lambert, Carlo Napolitano, Guy Lemaillet, Silvia G. PrioriAbstract:We identify a human mutation (E1053K) in the ankyrin-binding motif of Nav1.5 that is associated with Brugada syndrome, a fatal cardiac arrhythmia caused by altered function of Nav1.5. The E1053K mutation abolishes binding of Nav1.5 to ankyrin-G, and also prevents accumulation of Nav1.5 at cell surface sites in ventricular cardiomyocytes. Ankyrin-G and Nav1.5 are both localized at intercalated disc and T-tubule membranes in cardiomyocytes, and Nav1.5 coimmunoprecipitates with 190-kDa ankyrin-G from detergent-soluble lysates from rat heart. These data suggest that Nav1.5 associates with ankyrin-G and that ankyrin-G is required for Nav1.5 localization at excitable membranes in cardiomyocytes. Together with previous work in neurons, these results in cardiomyocytes suggest that ankyrin-G participates in a common pathway for localization of voltage-gated Nav channels at sites of function in multiple excitable cell types.
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physiological roles of axonal Ankyrins in survival of premyelinated axons and localization of voltage gated sodium channels
Journal of Neurocytology, 1999Co-Authors: Vann Bennett, Stephen LambertAbstract:440 kD ankyrin-B and 480/270 kD ankyrin-G are membrane skeletal proteins with closely related biochemical properties yet distinctive physiological roles in axons. These proteins associate with spectrin-actin networks and also bind to integral membrane proteins including the L1 CAM family of cell adhesion molecules and voltage-gated sodium channels. 440 kD ankyrin-B is expressed with L1 in premyelinated axon tracts, and is essential for survival of these axons, at least in the case of the optic nerve. 440 ankyrin-B may collaborate with L1 in transcellular structures that mediate axon fasciculation and mechanically stabilize axon bundles, although these proteins may also be involved in axon pathfinding. Ankyrin-B (−/−) mice exhibit loss of L1 from premyelinated axon tracts and a similar, although much more severe, phenotype to L1 (−/−) mice and humans with L1 mutations. Ankyrin-B and L1 thus are candidates to collaborate in the same structural pathway and defects in this pathway can lead to nervous system malformations and mental retardation. 480/270 kD ankyrin-G are highly concentrated along with the L1CAM family members neurofascin and NrCAM at nodes of Ranvier and axon initial segments. Voltage-gated sodium channels bind directly to Ankyrins, and are likely to associate in a ternary complex containing neurofascin/NrCAM, and ankyrin-G. Mice with ankyrin-G expression abolished in the cerebellum exhibit loss of ability of Purkinje neurons to fire action potentials, as well as loss of restriction of neurofascin/NrCAM to axon initial segments. Ankyrin-G thus is a key component in assembly of functional components of the axon initial segment and possibly the node of Ranvier.
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AnkyrinG Is Required for Clustering of Voltage-gated Na Channels at Axon Initial Segments and for Normal Action Potential Firing
Journal of Cell Biology, 1998Co-Authors: Daixing Zhou, Stephen Lambert, Peter L. Malen, Scott Carpenter, Linda M. Boland, Vann BennettAbstract:Voltage-gated sodium channels (NaCh) are colocalized with isoforms of the membrane-skeletal protein ankyrinG at axon initial segments, nodes of Ranvier, and postsynaptic folds of the mammalian neuromuscular junction. The role of ankyrinG in directing NaCh localization to axon initial segments was evaluated by region-specific knockout of ankyrinG in the mouse cerebellum. Mutant mice exhibited a progressive ataxia beginning around postnatal day P16 and subsequent loss of Purkinje neurons. In mutant mouse cerebella, NaCh were absent from axon initial segments of granule cell neurons, and Purkinje cells showed deficiencies in their ability to initiate action potentials and support rapid, repetitive firing. Neurofascin, a member of the L1CAM family of ankyrin-binding cell adhesion molecules, also exhibited impaired localization to initial segments of Purkinje cell neurons. These results demonstrate that ankyrinG is essential for clustering NaCh and neurofascin at axon initial segments and is required for physiological levels of sodium channel activity.
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molecular composition of the node of ranvier identification of ankyrin binding cell adhesion molecules neurofascin mucin third fniii domain and nrcam at nodal axon segments
Journal of Cell Biology, 1996Co-Authors: Jonathan Q. Davis, Stephen LambertAbstract:Neurofascin, NrCAM, L1, and NgCAM are a family of Ig/FNIII cell adhesion molecules that share ankyrin-binding activity in their cytoplasmic domains, and are candidates to form membrane-spanning complexes with members of the ankyrin family of spectrin-binding proteins in a variety of cellular contexts in the nervous system. Specialized forms of ankyrin, 270 kD and/or 480 kD ankyrinG are components of the membrane undercoat of axons at the node of Ranvier. This paper focuses on definition of the isoforms of ankyrin-binding cell adhesion molecules localized with ankyrinG at the nodal axon segment. The exon usage of two major forms of neurofascin was determined by isolation of full-length cDNAs and used to prepare isoform-specific antibodies. An isoform of neurofascin containing a mucin-like domain and lacking the third FNIII domain was concentrated at axon initial segments and colocalized at nodes of Ranvier with ankyrinG and the voltage-dependent sodium channel. An alternative form of neurofascin lacking the mucin-like domain and containing the third FNIII domain was present in unmyelinated axons. The antibody initially raised against neurofascin was used to screen a rat brain cDNA expression library. In addition to neurofascin, this screen yielded a clone with 80% sequence identity to NrCAM from chicken. The sequences of two full-length cDNAs are presented. NrCAM is most closely related to neurofascin among the other members of the L1/neurofascin/NgCAM family, with over 70% identity between cytoplasmic domains. NrCAM, visualized with antibodies specific for the ecto-domain, also was found to be coexpressed with neurofascin at nodes of Ranvier and at axon initial segments. This is the first characterization of defined neuronal cell adhesion molecules localized to axonal membranes at the node of Ranvier of myelinated axons.
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Chapter 7 Axonal Ankyrins and Ankyrin-Binding Proteins: Potential Participants in Lateral Membrane Domains and Transcellular Connections at the Node of Ranvier
Membrane Protein-Cytoskeleton Interactions, 1996Co-Authors: Stephen Lambert, Vann BennettAbstract:Publisher Summary This chapter examines the roles of axonal Ankyrins and ankyrin-binding proteins in the formation of lateral-membrane domains and transcellular connections at the node of Ranvier. Molecular interactions at the interface between extracellular and cytoplasmic compartments are believed to be of basic importance for establishment of lateral-membrane domains and formation of specialized sites of cell–cell contact. This interface is especially important for nerve axons, which require mechanisms for appropriate organization of ion channels involved in initiation and conductance of action potentials, and recognition systems for synaptogenesis during early development as well as to form specific contacts with glial cells along the length of axons. Nodes of Ranvier are flanked by intricate glial-cell processes and contain high concentrations of voltage-dependent sodium channels. Nodes of Ranvier of myelinated nerves are of considerable clinical interest because of their involvement in pathological conditions, including diabetic peripheral neuropathy and trauma; they are also the sites of regeneration of damaged peripheral nerve axons. Myelinated axons and nodes of Ranvier also exemplify several basic issues for cell biologists: formation of polarized cell domains, assembly of integral proteins into lateral-membrane domains, and formation of morphological structures that require cooperation between distinct types of cells.
Jonathan Q. Davis - One of the best experts on this subject based on the ideXlab platform.
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An ankyrin-based mechanism for functional organization of dystrophin and dystroglycan.
Cell, 2008Co-Authors: Gai Ayalon, Jonathan Q. Davis, Paula ScotlandAbstract:Summary β-dystroglycan (DG) and the dystrophin-glycoprotein complex (DGC) are localized at costameres and neuromuscular junctions in the sarcolemma of skeletal muscle. We present evidence for an ankyrin-based mechanism for sarcolemmal localization of dystrophin and β-DG. Dystrophin binds ankyrin-B and ankyrin-G, while β-DG binds ankyrin-G. Dystrophin and β-DG require ankyrin-G for retention at costameres but not delivery to the sarcolemma. Dystrophin and β-DG remain intracellular in ankyrin-B-depleted muscle, where β-DG accumulates in a juxta-TGN compartment. The neuromuscular junction requires ankyrin-B for localization of dystrophin/utrophin and β-DG and for maintenance of its postnatal morphology. A Becker muscular dystrophy mutation reduces ankyrin binding and impairs sarcolemmal localization of dystrophin-Dp71. Ankyrin-B also binds to dynactin-4, a dynactin subunit. Dynactin-4 and a subset of microtubules disappear from sarcolemmal sites in ankyrin-B-depleted muscle. Ankyrin-B thus is an adaptor required for sarcolemmal localization of dystrophin, as well as dynactin-4.
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Chapter 5 Ankyrins: A Family of Proteins that Link Diverse Membrane Proteins to the Spectrin Skeleton
Current Topics in Membranes, 2008Co-Authors: Vann Bennett, Jonathan Q. Davis, Lydia Davis, Ed Otto, Ekaterini KordeliAbstract:Publisher Summary Spectrin is a flexible rod-shaped molecule, comprising two subunits, aligned side-to-side to form hetero-dimers and head-to-head into tetramers that are capable of cross-linking actin, with binding sites, for actin on both ends. Two classes of protein interactions have been identified as an essential for the assembly of spectrin tetramers into a membrane-associated network; linkage of spectrin to the membrane and association of multiple spectrin molecules with actin to form a two-dimensional meshwork. Principal that can be derived, from the erythrocyte membrane, is that spectrin alone does not polymerize or assemble into higher order structures without the aid of accessory proteins. This chapter discusses Ankyrins that comprise an important class of spectrin-organizing proteins that are candidates to link a number of integral membrane proteins to the spectrin skeleton in specialized plasma membrane domains. The chapter discusses ankyrin structure of Ankyrins being a multigene family, functional diversity of ankyrin, because of alternative splicing of messenger RNA (mRNA) and of mapping the binding sites of ankyrin. Ankyrins are a family of structural proteins, associated with the plasma membrane, that are candidates to link integral membrane proteins to the spectrin skeleton. Ankyrin-binding proteins include three different ion channels: the anion exchanger of erythrocytes and kidney collecting ducts, the Na + /K + - adenosine triphosphate (ATP)ase of kidney distal tubules, and the voltage-dependent sodium channel of the brain.
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ankyrin g is a molecular partner of e cadherin in epithelial cells and early embryos
Journal of Biological Chemistry, 2007Co-Authors: Jonathan Q. Davis, Lydia Davis, Krishnakumar Kizhatil, Jan Hoffman, Brigid L M HoganAbstract:E-cadherin is a ubiquitous component of lateral membranes in epithelial tissues and is required to form the first lateral membrane domains in development. Here, we identify ankyrin-G as a molecular partner of E-cadherin and demonstrate that ankyrin-G and β-2-spectrin are required for accumulation of E-cadherin at the lateral membrane in both epithelial cells and early embryos. Ankyrin-G binds to the cytoplasmic domain of E-cadherin at a conserved site distinct from that of β-catenin. Ankyrin-G also recruits β-2-spectrin to E-cadherin-β-catenin complexes, thus providing a direct connection between E-cadherin and the spectrin/actin skeleton. In addition to restricting the membrane mobility of E-cadherin, ankyrin-G and β-2-spectrin also are required for exit of E-cadherin from the trans-Golgi network in a microtubule-dependent pathway. Ankyrin-G and β-2-spectrin co-localize with E-cadherin in preimplantation mouse embryos. Moreover, knockdown of either ankyrin-G or β-2-spectrin in one cell of a two-cell embryo blocks accumulation of E-cadherin at sites of cell-cell contact. E-cadherin thus requires both ankyrin-G and β-2-spectrin for its cellular localization in early embryos as well as cultured epithelial cells. We have recently reported that ankyrin-G and β-2-spectrin collaborate in biogenesis of the lateral membrane(Kizhatil, K., Yoon, W., Mohler, P. J., Davis, L. H., Hoffman, J. A., and Bennett, V. (2007)J. Biol. Chem. 282 2029-2037. Together with the current findings, these data suggest a ankyrin/spectrin-based mechanism for coordinating membrane assembly with extracellular interactions of E-cadherin at sites of cell-cell contact.
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ankyrin b coordinates the na k atpase na ca exchanger and insp3 receptor in a cardiac t tubule sr microdomain
PLOS Biology, 2005Co-Authors: Jonathan Q. DavisAbstract:We report identification of an ankyrin-B-based macromolecular complex of Na/K ATPase (alpha 1 and alpha 2 isoforms), Na/Ca exchanger 1, and InsP3 receptor that is localized in cardiomyocyte T-tubules in discrete microdomains distinct from classic dihydropyridine receptor/ryanodine receptor “dyads.” E1425G mutation of ankyrin-B, which causes human cardiac arrhythmia, also blocks binding of ankyrin-B to all three components of the complex. The ankyrin-B complex is markedly reduced in adult ankyrin-B+/− cardiomyocytes, which may explain elevated [Ca2+]i transients in these cells. Thus, loss of the ankyrin-B complex provides a molecular basis for cardiac arrhythmia in humans and mice. T-tubule-associated ankyrin-B, Na/Ca exchanger, and Na/K ATPase are not present in skeletal muscle, where ankyrin-B is expressed at 10-fold lower levels than in heart. Ankyrin-B also is not abundantly expressed in smooth muscle. We propose that the ankyrin-B-based complex is a specialized adaptation of cardiomyocytes with a role for cytosolic Ca2+ modulation.
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Isoform specificity among Ankyrins. An amphipathic alpha-helix in the divergent regulatory domain of ankyrin-b interacts with the molecular co-chaperone Hdj1/Hsp40.
The Journal of biological chemistry, 2004Co-Authors: Janis A. Hoffman, Jonathan Q. Davis, Khadar Abdi, Chong-rak Kim, Sarah K. Jones, Lydia Davis, Karen F. RobertsAbstract:Abstract Ankyrins-R, -B, and -G are a family of membrane-associated adaptors required for localization of structurally diverse proteins to specialized membrane domains, including axon initial segments, cardiomyocyte T-tubules, and epithelial cell lateral membranes. Ankyrins are often co-expressed in the same cells and, although structurally similar, have non-overlapping functions. We previously determined that the regulatory domain of ankyrin-B defines specificity between Ankyrins B and G in cardiomyocytes. Here, we identify key residues on the surface of an amphipathic α-helix unique to the regulatory domain of ankyrin-B that are essential for the function of ankyrin-B in cardiomyocytes. Using circular dichroism, we determined that a peptide representing the predicted helix folds as a helix in solution. Alanine-scanning mutagenesis revealed that residues 1773, 1777, 1780, 1784, and 1788 located in a patch on one surface the helix are critical for ankyrin-B function in cardiomyocytes. In a parallel set of experiments we determined that the molecular co-chaperone human DnaJ homologue 1 (Hdj1)/Hsp40 interacts with the ankyrin-B regulatory domain. Moreover, interaction of Hdj1/Hsp40 with the regulatory domain was mapped by random mutagenesis to same surface of the α-helix that is required for ankyrin-B function. These results provide new insight into the molecular basis for specificity between ankyrin-based pathways by defining a key α-helix structure in the divergent regulatory domain of ankyrin-B as well as interaction of the helix with Hdj1/Hsp40, the first downstream target for ankyrin-B-specific function.
Pietro De Camilli - One of the best experts on this subject based on the ideXlab platform.
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amphiphysin ii sh3p9 bin1 a member of the amphiphysin rvs family is concentrated in the cortical cytomatrix of axon initial segments and nodes of ranvier in brain and around t tubules in skeletal muscle
Journal of Cell Biology, 1997Co-Authors: Margaret H Butler, Carol David, Gian Carlo Ochoa, Zachary Freyberg, Laurie Daniell, Detlev Grabs, Ottavio Cremona, Pietro De CamilliAbstract:Amphiphysin (amphiphysin I), a dominant autoantigen in paraneoplastic Stiff-man syndrome, is a neuronal protein highly concentrated in nerve terminals, where it has a putative role in endocytosis. The yeast homologue of amphiphysin, Rvs167, has pleiotropic functions, including a role in endocytosis and in actin dynamics, suggesting that amphiphysin may also be implicated in the function of the presynaptic actin cytoskeleton. We report here the characterization of a second mammalian amphiphysin gene, amphiphysin II (SH3P9; BIN1), which encodes products primarily expressed in skeletal muscle and brain, as differentially spliced isoforms. In skeletal muscle, amphiphysin II is concentrated around T tubules, while in brain it is concentrated in the cytomatrix beneath the plasmamembrane of axon initial segments and nodes of Ranvier. In both these locations, amphiphysin II is colocalized with splice variants of ankyrin3 (ankyrinG), a component of the actin cytomatrix. In the same regions, the presence of clathrin has been reported. These findings support the hypothesis that, even in mammalian cells, amphiphysin/Rvs family members have a role both in endocytosis and in actin function and suggest that distinct amphiphysin isoforms contribute to define distinct domains of the cortical cytoplasm. Since amphiphysin II (BIN1) was reported to interact with Myc, it may also be implicated in a signaling pathway linking the cortical cytoplasm to nuclear function.
Ekaterini Kordeli - One of the best experts on this subject based on the ideXlab platform.
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novel interactions of Ankyrins g at the costameres the muscle specific obscurin titin binding related domain otbd binds plectin and filamin c
Experimental Cell Research, 2011Co-Authors: Yimingjiang Maiweilidan, Ekaterini Kordeli, Izabela KlauzaAbstract:Abstract Ankyrins, the adapters of the spectrin skeleton, are involved in local accumulation and stabilization of integral proteins to the appropriate membrane domains. In striated muscle, tissue-dependent alternative splicing generates unique Ank3 gene products (Ankyrins-G); they share the Obscurin/Titin-Binding-related Domain (OTBD), a muscle-specific insert of the C-terminal domain which is highly conserved among ankyrin genes, and binds obscurin and titin to Ank1 gene products. We previously proposed that OTBD sequences constitute a novel domain of protein–protein interactions which confers Ankyrins with specific cellular functions in muscle. Here we searched for muscle proteins binding to ankyrin-G OTBD by yeast two hybrid assay, and we found plectin and filamin C, two organizing elements of the cytoskeleton with essential roles in myogenesis, muscle cell cytoarchitecture, and muscle disease. The three proteins coimmunoprecipitate from skeletal muscle extracts and colocalize at costameres in adult muscle fibers. During in vitro myogenesis, muscle Ankyrins-G are first expressed in postmitotic myocytes undergoing fusion to myotubes. In western blots of subcellular fractions from C2C12 cells, the majority of muscle Ankyrins-G appear associated with membrane compartments. Occasional but not extensive co-localization at nascent costameres suggested that ankyrin-G interactions with plectin and filamin C are not involved in costamere assembly; they would rather reinforce stability and/or modulate molecular interactions in sarcolemma microdomains by establishing novel links between muscle-specific Ankyrins-G and the two costameric dystrophin-associated glycoprotein and integrin-based protein complexes. These results report the first protein–protein interactions involving the ankyrin-G OTBD domain and support the hypothesis that OTBD sequences confer Ankyrins with a gain of function in vertebrates, bringing further consolidation and resilience of the linkage between sarcomeres and sarcolemma.
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Chapter 5 Ankyrins: A Family of Proteins that Link Diverse Membrane Proteins to the Spectrin Skeleton
Current Topics in Membranes, 2008Co-Authors: Vann Bennett, Jonathan Q. Davis, Lydia Davis, Ed Otto, Ekaterini KordeliAbstract:Publisher Summary Spectrin is a flexible rod-shaped molecule, comprising two subunits, aligned side-to-side to form hetero-dimers and head-to-head into tetramers that are capable of cross-linking actin, with binding sites, for actin on both ends. Two classes of protein interactions have been identified as an essential for the assembly of spectrin tetramers into a membrane-associated network; linkage of spectrin to the membrane and association of multiple spectrin molecules with actin to form a two-dimensional meshwork. Principal that can be derived, from the erythrocyte membrane, is that spectrin alone does not polymerize or assemble into higher order structures without the aid of accessory proteins. This chapter discusses Ankyrins that comprise an important class of spectrin-organizing proteins that are candidates to link a number of integral membrane proteins to the spectrin skeleton in specialized plasma membrane domains. The chapter discusses ankyrin structure of Ankyrins being a multigene family, functional diversity of ankyrin, because of alternative splicing of messenger RNA (mRNA) and of mapping the binding sites of ankyrin. Ankyrins are a family of structural proteins, associated with the plasma membrane, that are candidates to link integral membrane proteins to the spectrin skeleton. Ankyrin-binding proteins include three different ion channels: the anion exchanger of erythrocytes and kidney collecting ducts, the Na + /K + - adenosine triphosphate (ATP)ase of kidney distal tubules, and the voltage-dependent sodium channel of the brain.
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ankyring a new ankyrin gene with neural specific isoforms localized at the axonal initial segment and node of ranvier
Journal of Biological Chemistry, 1995Co-Authors: Ekaterini Kordeli, Stephen LambertAbstract:We have characterized a new ankyrin gene, expressed in brain and other tissues, that is subject to extensive tissue-specific alternative mRNA processing. The full-length polypeptide has a molecular mass of 480 kDa and includes a predicted globular head domain, with membrane- and spectrin-binding activities, as well as an extended "tail" domain. We term this gene ankyrinG based on its giant size and general expression. Two brain-specific isoforms of 480 kDa and 270 kDa were identified that contain a unique stretch of sequence highly enriched in serine and threonine residues immediately following the globular head domain. Antibodies against the serine-rich domain and spectrin-binding domain revealed labeling of nodes of Ranvier and axonal initial segments. Ankyrin-binding proteins also known to be localized in these specialized membrane domains include the voltage-dependent sodium channel, the sodium/potassium ATPase, sodium/calcium exchanger, and members of the neurofascin/L1 family of cell adhesion molecules. The neural-specific ankyrinG polypeptides are candidates to participate in maintenance/targeting of ion channels and cell adhesion molecules to nodes of Ranvier and axonal initial segments.