1
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Pochampally S, Hartman KL, Wang R, Wang J, Yun MK, Parmar K, Park H, Meibohm B, White SW, Li W, Miller DD. Design, Synthesis, and Biological Evaluation of Pyrimidine Dihydroquinoxalinone Derivatives as Tubulin Colchicine Site-Binding Agents That Displayed Potent Anticancer Activity Both In Vitro and In Vivo. ACS Pharmacol Transl Sci 2023; 6:526-545. [PMID: 37082747 PMCID: PMC10111625 DOI: 10.1021/acsptsci.2c00108] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Indexed: 04/22/2023]
Abstract
Polymerization of tubulin dimers to form microtubules is one of the key events in cell proliferation. The inhibition of this event has long been recognized as a potential treatment option for various types of cancer. Compound 1e was previously developed by our team as a potent inhibitor of tubulin polymerization that binds to the colchicine site. To further improve the potency and therapeutic properties of compound 1e, we hypothesized based on the X-ray crystal structure that modification of the pyrimidine dihydroquinoxalinone scaffold with additional hetero-atom (N, O, and S) substituents could allow the resulting new compounds to bind more tightly to the colchicine site and display greater efficacy in cancer therapy. We therefore synthesized a series of new pyrimidine dihydroquinoxalinone derivatives, compounds 10, 12b-c, 12e, 12h, and 12j-l, and evaluated their cytotoxicity and relative ability to inhibit proliferation, resulting in the discovery of new tubulin-polymerization inhibitors. Among these, the most potent new inhibitor was compound 12k, which exhibited high cytotoxic activity in vitro, a longer half-life than the parental compound in liver microsomes (IC50 = 0.2 nM, t 1/2 = >300 min), and significant potency against a wide range of cancer cell lines including those from melanoma and breast, pancreatic, and prostate cancers. High-resolution X-ray crystal structures of the best compounds in this scaffold series, 12e, 12j, and 12k, confirmed their direct binding to the colchicine site of tubulin and revealed their detailed molecular interactions. Further evaluation of 12k in vivo using a highly taxane-resistant prostate cancer xenograft model, PC-3/TxR, demonstrated the strong tumor growth inhibition at the low dose of 2.5 mg/kg (i.v., twice per week). Collectively, these results strongly support further preclinical evaluations of 12k as a potential candidate for development.
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Affiliation(s)
- Satyanarayana Pochampally
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Kelli L. Hartman
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Rui Wang
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Jiaxing Wang
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Mi-Kyung Yun
- Department
of Structural Biology, St. Jude Children’s
Research Hospital, Memphis, Tennessee 38105, United States
| | - Keyur Parmar
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Hyunseo Park
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Bernd Meibohm
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Stephen W. White
- Department
of Structural Biology, St. Jude Children’s
Research Hospital, Memphis, Tennessee 38105, United States
| | - Wei Li
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Duane D. Miller
- Department
of Pharmaceutical Sciences, University of
Tennessee Health Science Center, Memphis, Tennessee 38163, United States
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2
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Chen H, Deng S, Albadari N, Yun MK, Zhang S, Li Y, Ma D, Parke DN, Yang L, Seagroves TN, White SW, Miller DD, Li W. Design, Synthesis, and Biological Evaluation of Stable Colchicine-Binding Site Tubulin Inhibitors 6-Aryl-2-benzoyl-pyridines as Potential Anticancer Agents. J Med Chem 2021; 64:12049-12074. [PMID: 34378386 PMCID: PMC9206500 DOI: 10.1021/acs.jmedchem.1c00715] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We previously reported a potent tubulin inhibitor CH-2-77. In this study, we optimized the structure of CH-2-77 by blocking metabolically labile sites and synthesized a series of CH-2-77 analogues. Two compounds, 40a and 60c, preserved the potency while improving the metabolic stability over CH-2-77 by 3- to 4-fold (46.8 and 29.4 vs 10.8 min in human microsomes). We determined the high-resolution X-ray crystal structures of 40a (resolution 2.3 Å) and 60c (resolution 2.6 Å) in complex with tubulin and confirmed their direct binding at the colchicine-binding site. In vitro, 60c maintained its mode of action by inhibiting tubulin polymerization and was effective against P-glycoprotein-mediated multiple drug resistance and taxol resistance. In vivo, 60c exhibited a strong inhibitory effect on tumor growth and metastasis in a taxol-resistant A375/TxR xenograft model without obvious toxicity. Collectively, this work showed that 60c is a promising lead compound for further development as a potential anticancer agent.
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Affiliation(s)
- Hao Chen
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Shanshan Deng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Najah Albadari
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Mi-Kyung Yun
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, United States
| | - Sicheng Zhang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Yong Li
- Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, United States
| | - Dejian Ma
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Deanna N Parke
- Department of Pathology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Lei Yang
- Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, United States
| | - Tiffany N Seagroves
- Department of Pathology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Stephen W White
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, United States
| | - Duane D Miller
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
| | - Wei Li
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States
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3
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Chen J, Kholina E, Szyk A, Fedorov VA, Kovalenko I, Gudimchuk N, Roll-Mecak A. α-tubulin tail modifications regulate microtubule stability through selective effector recruitment, not changes in intrinsic polymer dynamics. Dev Cell 2021; 56:2016-2028.e4. [PMID: 34022132 PMCID: PMC8476856 DOI: 10.1016/j.devcel.2021.05.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 04/26/2021] [Accepted: 05/05/2021] [Indexed: 10/21/2022]
Abstract
Microtubules are non-covalent polymers of αβ-tubulin dimers. Posttranslational processing of the intrinsically disordered C-terminal α-tubulin tail produces detyrosinated and Δ2-tubulin. Although these are widely employed as proxies for stable cellular microtubules, their effect (and of the α-tail) on microtubule dynamics remains uncharacterized. Using recombinant, engineered human tubulins, we now find that neither detyrosinated nor Δ2-tubulin affect microtubule dynamics, while the α-tubulin tail is an inhibitor of microtubule growth. Consistent with the latter, molecular dynamics simulations show the α-tubulin tail transiently occluding the longitudinal microtubule polymerization interface. The marked differential in vivo stabilities of the modified microtubule subpopulations, therefore, must result exclusively from selective effector recruitment. We find that tyrosination quantitatively tunes CLIP-170 density at the growing plus end and that CLIP170 and EB1 synergize to selectively upregulate the dynamicity of tyrosinated microtubules. Modification-dependent recruitment of regulators thereby results in microtubule subpopulations with distinct dynamics, a tenet of the tubulin code hypothesis.
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Affiliation(s)
- Jiayi Chen
- Cell Biology and Biophysics Unit, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | - Ekaterina Kholina
- Department of Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Agnieszka Szyk
- Cell Biology and Biophysics Unit, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | - Vladimir A Fedorov
- Department of Biology, Lomonosov Moscow State University, Moscow, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Russian Academy of Sciences, Moscow, Russia
| | - Ilya Kovalenko
- Department of Biology, Lomonosov Moscow State University, Moscow, Russia; Astrakhan State University, Astrakhan 414056, Russia; Sechenov University, Moscow 119991, Russia
| | - Nikita Gudimchuk
- Department of Physics, Lomonosov Moscow State University, Moscow, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Russian Academy of Sciences, Moscow, Russia; Dmitry Rogachev National Research Center of Pediatric Hematology, Oncology and Immunology, Moscow, Russia.
| | - Antonina Roll-Mecak
- Cell Biology and Biophysics Unit, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA; Biochemistry and Biophysics Center, National Heart Lung and Blood Institute, Bethesda, MD 20892, USA.
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4
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Fung HYJ, McKibben KM, Ramirez J, Gupta K, Rhoades E. Structural Characterization of Tau in Fuzzy Tau:Tubulin Complexes. Structure 2020; 28:378-384.e4. [PMID: 31995742 DOI: 10.1016/j.str.2020.01.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 11/21/2019] [Accepted: 01/07/2020] [Indexed: 02/02/2023]
Abstract
Tau is a neuronal microtubule (MT)-associated protein of significant interest due to its association with several neurodegenerative disorders. Tau's intrinsic disorder and the dynamic nature of its interactions with tubulin and MTs make its structural characterization challenging. Here, we use an environmentally sensitive fluorophore as a site-specific probe of tau bound to soluble tubulin. Comparison of our results with a recently published tau:MT cryoelectron microscopy model reveals structural similarities between tubulin- and MT-bound tau. Analysis of residues across the repeat regions reveals a hierarchy in tubulin occupancy, which may be relevant to tau's ability to differentiate between tubulin and MTs. As binding to soluble tubulin is a critical first step in MT polymerization, our characterization of the structural features of tau in dynamic, fuzzy tau:tubulin assemblies advances our understanding of how tau functions in the cell and how function may be disrupted in disease.
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Affiliation(s)
- Ho Yee Joyce Fung
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Kristen M McKibben
- Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine at University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Jennifer Ramirez
- Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine at University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Kushol Gupta
- Department of Biochemistry and Biophysics, Perelman School of Medicine at University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Elizabeth Rhoades
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA; Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine at University of Pennsylvania, Philadelphia, PA 19104, USA.
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5
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Lessard DV, Zinder OJ, Hotta T, Verhey KJ, Ohi R, Berger CL. Polyglutamylation of tubulin's C-terminal tail controls pausing and motility of kinesin-3 family member KIF1A. J Biol Chem 2019; 294:6353-6363. [PMID: 30770469 DOI: 10.1074/jbc.ra118.005765] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Revised: 02/11/2019] [Indexed: 01/06/2023] Open
Abstract
The kinesin-3 family member KIF1A plays a critical role in site-specific neuronal cargo delivery during axonal transport. KIF1A cargo is mislocalized in many neurodegenerative diseases, indicating that KIF1A's highly efficient, superprocessive motility along axonal microtubules needs to be tightly regulated. One potential regulatory mechanism may be through posttranslational modifications (PTMs) of axonal microtubules. These PTMs often occur on the C-terminal tails of the microtubule tracks, act as molecular "traffic signals" helping to direct kinesin motor cargo delivery, and include C-terminal tail polyglutamylation important for KIF1A cargo transport. KIF1A initially interacts with microtubule C-terminal tails through its K-loop, a positively charged surface loop of the KIF1A motor domain. However, the role of the K-loop in KIF1A motility and response to perturbations in C-terminal tail polyglutamylation is underexplored. Using single-molecule imaging, we present evidence that KIF1A pauses on different microtubule lattice structures, linking multiple processive segments together and contributing to KIF1A's characteristic superprocessive run length. Furthermore, modifications of the KIF1A K-loop or tubulin C-terminal tail polyglutamylation reduced KIF1A pausing and overall run length. These results suggest a new mechanism to regulate KIF1A motility via pauses mediated by K-loop/polyglutamylated C-terminal tail interactions, providing further insight into KIF1A's role in axonal transport.
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Affiliation(s)
- Dominique V Lessard
- From the Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405 and
| | - Oraya J Zinder
- From the Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405 and
| | - Takashi Hotta
- the Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109
| | - Kristen J Verhey
- the Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109
| | - Ryoma Ohi
- the Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109
| | - Christopher L Berger
- From the Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405 and
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6
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Shemesh A, Ginsburg A, Levi-Kalisman Y, Ringel I, Raviv U. Structure, Assembly, and Disassembly of Tubulin Single Rings. Biochemistry 2018; 57:6153-6165. [PMID: 30247898 DOI: 10.1021/acs.biochem.8b00560] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Single and double tubulin rings were studied under a range of conditions and during microtubule (MT) assembly and disassembly. Here, tubulin was purified from porcine brain and used without any further modifications or additives that promote ring assembly. The structure of single GDP-rich tubulin rings was determined by cryo-transmission electron microscopy and synchrotron solution X-ray scattering. The scattering curves were fitted to atomic models, using our state-of-the-art analysis software, D+ . We found that there is a critical concentration for ring formation, which increased with GTP concentration with temperature. MT assembly or disassembly, induced by changes in temperature, was analyzed by time-resolved small-angle X-ray scattering. During MT assembly, the fraction of rings and unassembled dimers simultaneously decreased. During MT disassembly, the mass fraction of dimers increased. The increase in the concentration of rings was delayed until the fraction of dimers was sufficiently high. We verified that pure dimers, eluted via size-exclusion chromatography, could also form rings. Interestingly, X-ray radiation triggered tubulin ring disassembly. The concentration of disassembled rings versus exposure time followed a first-order kinetics. The disassembly rate constant and initial concentration were determined. X-ray radiation-triggered disassembly was used to determine the concentration of rings. We confirmed that following a temperature jump, the mass fraction of rings decreased and then stabilized at a constant value during the first stage of the MT assembly kinetics. This study sheds light on the most basic assembly and disassembly conditions for in vitro single GDP-rich tubulin rings and their relation to MT kinetics.
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Affiliation(s)
- Asaf Shemesh
- Institute of Chemistry , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel.,Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel
| | - Avi Ginsburg
- Institute of Chemistry , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel.,Institute for Drug Research, School of Pharmacy , The Hebrew University of Jerusalem , Jerusalem 9112102 , Israel
| | - Yael Levi-Kalisman
- Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel.,Institute of Life Sciences , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel
| | - Israel Ringel
- Institute for Drug Research, School of Pharmacy , The Hebrew University of Jerusalem , Jerusalem 9112102 , Israel
| | - Uri Raviv
- Institute of Chemistry , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel.,Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel
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7
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Wang D, Nitta R, Morikawa M, Yajima H, Inoue S, Shigematsu H, Kikkawa M, Hirokawa N. Motility and microtubule depolymerization mechanisms of the Kinesin-8 motor, KIF19A. eLife 2016; 5. [PMID: 27690357 PMCID: PMC5045296 DOI: 10.7554/elife.18101] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Accepted: 09/08/2016] [Indexed: 12/20/2022] Open
Abstract
The kinesin-8 motor, KIF19A, accumulates at cilia tips and controls cilium length. Defective KIF19A leads to hydrocephalus and female infertility because of abnormally elongated cilia. Uniquely among kinesins, KIF19A possesses the dual functions of motility along ciliary microtubules and depolymerization of microtubules. To elucidate the molecular mechanisms of these functions we solved the crystal structure of its motor domain and determined its cryo-electron microscopy structure complexed with a microtubule. The features of KIF19A that enable its dual function are clustered on its microtubule-binding side. Unexpectedly, a destabilized switch II coordinates with a destabilized L8 to enable KIF19A to adjust to both straight and curved microtubule protofilaments. The basic clusters of L2 and L12 tether the microtubule. The long L2 with a characteristic acidic-hydrophobic-basic sequence effectively stabilizes the curved conformation of microtubule ends. Hence, KIF19A utilizes multiple strategies to accomplish the dual functions of motility and microtubule depolymerization by ATP hydrolysis. DOI:http://dx.doi.org/10.7554/eLife.18101.001 The cells that line the airways and other passages in the body have hair-like structures called cilia on their surface. Maintaining the cilia at an appropriate length is key to allowing fluid to flow efficiently in these passages. A protein called tubulin forms scaffolds known as microtubules that give each cilium its shape and allow it to change length. Motor proteins are also found in cilia, and travel along the microtubules to transport substances. One of these microtubule-based motors, referred to as KIF19A, accumulates at the tip of cilia and controls their length. It does so by combining two actions: it moves along the microtubule to the tip of the cilium, and then removes tubulin molecules from the end. Microtubules are straight along their length and curved at the end, and it is thought that kinesin recognizes both of these shapes in order to carry out these roles. A single region of the KIF19A protein appears to be able to accomplish both roles, but the molecular changes that the protein undergoes to do so are not known. Wang et al. have now investigated these changes by determining the structure of the motor domain of KIF19A from mice using two experimental approaches: X-ray crystallography and cryo-electron microscopy. These structures showed that the specific structural features responsible for the protein's dual roles are indeed clustered on the side of the protein that binds to the microtubule. Wang et al. also identified the regions that make KIF19A flexible enough to fit this interface with both straight and curved microtubules. Next, Wang et al. found that other regions of KIF19A stop it detaching from the microtubule and allow it to stabilize the curved shape of microtubule ends; this stimulates the microtubule to disassemble, or “depolymerize”. The findings show that KIF19A uses multiple strategies to enable it to carry out its roles. To understand better how KIF19A depolymerizes the microtubule, a more detailed structure of KIF19A together with tubulin will be needed. Structural studies of KIF19A in cilia will also be useful to understand how the protein controls the length of microtubules. DOI:http://dx.doi.org/10.7554/eLife.18101.002
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Affiliation(s)
- Doudou Wang
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Department of Molecular Structure and Dynamics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Ryo Nitta
- RIKEN Center for Life Science Technologies, Yokohama, Japan
| | - Manatsu Morikawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Department of Molecular Structure and Dynamics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Hiroaki Yajima
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Department of Molecular Structure and Dynamics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Shigeyuki Inoue
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Department of Molecular Structure and Dynamics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | | | - Masahide Kikkawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Nobutaka Hirokawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Department of Molecular Structure and Dynamics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Center of Excellence in Genomic Medicine Research, King Abdulaziz University, Jeddah, Saudi Arabia
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8
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Di Maïo IL, Barbier P, Allegro D, Brault C, Peyrot V. Quantitative analysis of tau-microtubule interaction using FRET. Int J Mol Sci 2014; 15:14697-714. [PMID: 25196605 PMCID: PMC4159876 DOI: 10.3390/ijms150814697] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 06/30/2014] [Accepted: 07/14/2014] [Indexed: 11/23/2022] Open
Abstract
The interaction between the microtubule associated protein, tau and the microtubules is investigated. A fluorescence resonance energy transfer (FRET) assay was used to determine the distance separating tau to the microtubule wall, as well as the binding parameters of the interaction. By using microtubules stabilized with Flutax-2 as donor and tau labeled with rhodamine as acceptor, a donor-to-acceptor distance of 54 ± 1 Å was found. A molecular model is proposed in which Flutax-2 is directly accessible to tau-rhodamine molecules for energy transfer. By titration, we calculated the stoichiometric dissociation constant to be equal to 1.0 ± 0.5 µM. The influence of the C-terminal tails of αβ-tubulin on the tau-microtubule interaction is presented once a procedure to form homogeneous solution of cleaved tubulin has been determined. The results indicate that the C-terminal tails of α- and β-tubulin by electrostatic effects and of recruitment seem to be involved in the binding mechanism of tau.
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Affiliation(s)
- Isabelle L Di Maïo
- Aix-Marseille Université, Inserm, CRO2 UMR_S 911, Faculté de Pharmacie, 27 Bd Jean Moulin, 13385 Marseille, France
| | - Pascale Barbier
- Aix-Marseille Université, Inserm, CRO2 UMR_S 911, Faculté de Pharmacie, 27 Bd Jean Moulin, 13385 Marseille, France.
| | - Diane Allegro
- Aix-Marseille Université, Inserm, CRO2 UMR_S 911, Faculté de Pharmacie, 27 Bd Jean Moulin, 13385 Marseille, France.
| | - Cédric Brault
- Aix-Marseille Université, Inserm, CRO2 UMR_S 911, Faculté de Pharmacie, 27 Bd Jean Moulin, 13385 Marseille, France.
| | - Vincent Peyrot
- Aix-Marseille Université, Inserm, CRO2 UMR_S 911, Faculté de Pharmacie, 27 Bd Jean Moulin, 13385 Marseille, France.
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9
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Lazarus JE, Moughamian AJ, Tokito MK, Holzbaur ELF. Dynactin subunit p150(Glued) is a neuron-specific anti-catastrophe factor. PLoS Biol 2013; 11:e1001611. [PMID: 23874158 PMCID: PMC3712912 DOI: 10.1371/journal.pbio.1001611] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Accepted: 05/31/2013] [Indexed: 01/25/2023] Open
Abstract
The dynein partner dynactin not only binds to microtubules, but is found to potently influence microtubule dynamics in neurons. Regulation of microtubule dynamics in neurons is critical, as defects in the microtubule-based transport of axonal organelles lead to neurodegenerative disease. The microtubule motor cytoplasmic dynein and its partner complex dynactin drive retrograde transport from the distal axon. We have recently shown that the p150Glued subunit of dynactin promotes the initiation of dynein-driven cargo motility from the microtubule plus-end. Because plus end-localized microtubule-associated proteins like p150Glued may also modulate the dynamics of microtubules, we hypothesized that p150Glued might promote cargo initiation by stabilizing the microtubule track. Here, we demonstrate in vitro using assembly assays and TIRF microscopy, and in primary neurons using live-cell imaging, that p150Glued is a potent anti-catastrophe factor for microtubules. p150Glued alters microtubule dynamics by binding both to microtubules and to tubulin dimers; both the N-terminal CAP-Gly and basic domains of p150Glued are required in tandem for this activity. p150Glued is alternatively spliced in vivo, with the full-length isoform including these two domains expressed primarily in neurons. Accordingly, we find that RNAi of p150Glued in nonpolarized cells does not alter microtubule dynamics, while depletion of p150Glued in neurons leads to a dramatic increase in microtubule catastrophe. Strikingly, a mutation in p150Glued causal for the lethal neurodegenerative disorder Perry syndrome abrogates this anti-catastrophe activity. Thus, we find that dynactin has multiple functions in neurons, both activating dynein-mediated retrograde axonal transport and enhancing microtubule stability through a novel anti-catastrophe mechanism regulated by tissue-specific isoform expression; disruption of either or both of these functions may contribute to neurodegenerative disease. Microtubules are polymers of tubulin that undergo successive cycles of growth and shrinkage so that the cell can maintain a stable yet adaptable cytoskeleton. In neurons, the microtubule motor protein dynein and its partner complex dynactin drive retrograde transport along microtubules from the distal axon towards the cell body. In addition to binding to dynein, the p150Glued subunit of dynactin independently binds directly to microtubules. We hypothesized that by binding to microtubules, p150Glued might also alter microtubule dynamics. We demonstrate using biochemistry and microscopy in vitro and in cells that p150Glued stabilizes microtubules by inhibiting the transition from growth to shrinkage. We show that specific domains of p150Glued encoded by neuronally enriched splice-forms are necessary for this activity. Although depletion of p150Glued in nonpolarized cells does not alter microtubule dynamics, depletion of endogenous p150Glued in neurons leads to dramatic microtubule instability. Strikingly, a mutation in p150Glued known to cause the neurodegenerative disorder Perry syndrome abolishes this activity. In summary, we identified a previously unappreciated function of dynactin in direct regulation of the microtubule cytoskeleton. This activity may enhance generic microtubule stability in the cell, but could be especially important in specific areas of the cell where dynactin and dynein are loaded onto microtubules.
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Affiliation(s)
- Jacob E. Lazarus
- Department of Physiology and Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Armen J. Moughamian
- Department of Physiology and Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Mariko K. Tokito
- Department of Physiology and Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Erika L. F. Holzbaur
- Department of Physiology and Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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10
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Zhang X, Wang H, Duvernay MT, Zhu S, Wu G. The angiotensin II type 1 receptor C-terminal Lys residues interact with tubulin and modulate receptor export trafficking. PLoS One 2013; 8:e57805. [PMID: 23451270 PMCID: PMC3581488 DOI: 10.1371/journal.pone.0057805] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 01/25/2013] [Indexed: 12/15/2022] Open
Abstract
The physiological and pathological functions of angiotensin II are largely mediated through activating the cell surface angiotensin II type 1 receptor (AT1R). However, the molecular mechanisms underlying the transport of newly synthesized AT1R from the endoplasmic reticulum (ER) to the cell surface remain poorly defined. Here we demonstrated that the C-terminus (CT) of AT1R directly and strongly bound to tubulin and the binding domains were mapped to two consecutive Lys residues at positions 310 and 311 in the CT membrane-proximal region of AT1R and the acidic CT of tubulin, suggestive of essentially ionic interactions between AT1R and tubulin. Furthermore, mutation to disrupt tubulin binding dramatically inhibited the cell surface expression of AT1R, arrested AT1R in the ER, and attenuated AT1R-mediated signaling measured as ERK1/2 activation. These data demonstrate for the first time that specific Lys residues in the CT juxtamembrane region regulate the processing of AT1R through interacting with tubulin. These data also suggest an important role of the microtubule network in the cell surface transport of AT1R.
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Affiliation(s)
- Xiaoping Zhang
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana, United States of America
| | - Hong Wang
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana, United States of America
- School of Life Sciences and Technology, Tongji University, Shanghai, China
| | - Matthew T. Duvernay
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana, United States of America
| | - Shu Zhu
- Department of Pharmacology and Toxicology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia, United States of America
| | - Guangyu Wu
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana, United States of America
- Department of Pharmacology and Toxicology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia, United States of America
- * E-mail:
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11
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Shen QT, Hsiue PP, Sindelar CV, Welch MD, Campellone KG, Wang HW. Structural insights into WHAMM-mediated cytoskeletal coordination during membrane remodeling. ACTA ACUST UNITED AC 2013; 199:111-24. [PMID: 23027905 PMCID: PMC3461504 DOI: 10.1083/jcb.201204010] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Structural analysis of the WHAMM–microtubule interaction provides insight into WHAMM’s coordination of microtubule binding, membrane association, and actin nucleation. The microtubule (MT) and actin cytoskeletons drive many essential cellular processes, yet fairly little is known about how their functions are coordinated. One factor that mediates important cross talk between these two systems is WHAMM, a Golgi-associated protein that utilizes MT binding and actin nucleation activities to promote membrane tubulation during intracellular transport. Using cryoelectron microscopy and other biophysical and biochemical approaches, we unveil the underlying mechanisms for how these activities are coordinated. We find that WHAMM bound to the outer surface of MT protofilaments via a novel interaction between its central coiled-coil region and tubulin heterodimers. Upon the assembly of WHAMM onto MTs, its N-terminal membrane-binding domain was exposed at the MT periphery, where it can recruit vesicles and remodel them into tubular structures. In contrast, MT binding masked the C-terminal portion of WHAMM and prevented it from promoting actin nucleation. These results give rise to a model whereby distinct MT-bound and actin-nucleating populations of WHAMM collaborate during membrane tubulation.
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Affiliation(s)
- Qing-Tao Shen
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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12
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Pecqueur L, Duellberg C, Dreier B, Jiang Q, Wang C, Plückthun A, Surrey T, Gigant B, Knossow M. A designed ankyrin repeat protein selected to bind to tubulin caps the microtubule plus end. Proc Natl Acad Sci U S A 2012; 109:12011-6. [PMID: 22778434 PMCID: PMC3409770 DOI: 10.1073/pnas.1204129109] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Microtubules are cytoskeleton filaments consisting of αβ-tubulin heterodimers. They switch between phases of growth and shrinkage. The underlying mechanism of this property, called dynamic instability, is not fully understood. Here, we identified a designed ankyrin repeat protein (DARPin) that interferes with microtubule assembly in a unique manner. The X-ray structure of its complex with GTP-tubulin shows that it binds to the β-tubulin surface exposed at microtubule (+) ends. The details of the structure provide insight into the role of GTP in microtubule polymerization and the conformational state of tubulin at the very microtubule end. They show in particular that GTP facilitates the tubulin structural switch that accompanies microtubule assembly but does not trigger it in unpolymerized tubulin. Total internal reflection fluorescence microscopy revealed that the DARPin specifically blocks growth at the microtubule (+) end by a selective end-capping mechanism, ultimately favoring microtubule disassembly from that end. DARPins promise to become designable tools for the dissection of microtubule dynamic properties selective for either of their two different ends.
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Affiliation(s)
- Ludovic Pecqueur
- Laboratoire d’Enzymologie et Biochimie Structurales, Centre de Recherche de Gif, Centre National de la Recherche Scientifique, 91198 Gif sur Yvette, France
| | - Christian Duellberg
- Microtubule Cytoskeleton Laboratory, London Research Institute, Cancer Research United Kingdom, London WC2A 4LY, United Kingdom
| | - Birgit Dreier
- Department of Biochemistry, University of Zurich, CH-8057 Zurich, Switzerland; and
| | - Qiyang Jiang
- Institute of Protein Research, School of Life Sciences and Technology, Tongji University, Shanghai 200092, China
| | - Chunguang Wang
- Institute of Protein Research, School of Life Sciences and Technology, Tongji University, Shanghai 200092, China
| | - Andreas Plückthun
- Department of Biochemistry, University of Zurich, CH-8057 Zurich, Switzerland; and
| | - Thomas Surrey
- Microtubule Cytoskeleton Laboratory, London Research Institute, Cancer Research United Kingdom, London WC2A 4LY, United Kingdom
| | - Benoît Gigant
- Laboratoire d’Enzymologie et Biochimie Structurales, Centre de Recherche de Gif, Centre National de la Recherche Scientifique, 91198 Gif sur Yvette, France
| | - Marcel Knossow
- Laboratoire d’Enzymologie et Biochimie Structurales, Centre de Recherche de Gif, Centre National de la Recherche Scientifique, 91198 Gif sur Yvette, France
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13
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Mignot I, Pecqueur L, Dorléans A, Karuppasamy M, Ravelli RBG, Dreier B, Plückthun A, Knossow M, Gigant B. Design and characterization of modular scaffolds for tubulin assembly. J Biol Chem 2012; 287:31085-94. [PMID: 22791712 DOI: 10.1074/jbc.m112.383869] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In cells, microtubule dynamics is regulated by stabilizing and destabilizing factors. Whereas proteins in both categories have been identified, their mechanism of action is rarely understood at the molecular level. This is due in part to the difficulties faced in structural approaches to obtain atomic models when tubulin is involved. Here, we design and characterize new stathmin-like domain (SLD) proteins that sequester tubulins in numbers different from two, the number of tubulins bound by stathmin or by the SLD of RB3, two stathmin family members that have been extensively studied. We established rules for the design of tight tubulin-SLD assemblies and applied them to complexes containing one to four tubulin heterodimers. Biochemical and structural experiments showed that the engineered SLDs behaved as expected. The new SLDs will be tools for structural studies of microtubule regulation. The larger complexes will be useful for cryo-electron microscopy, whereas crystallography or nuclear magnetic resonance will benefit from the 1:1 tubulin-SLD assembly. Finally, our results provide new insight into SLD function, suggesting that a major effect of these phosphorylatable proteins is the programmed release of sequestered tubulin for microtubule assembly at the specific cellular locations of members of the stathmin family.
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Affiliation(s)
- Ingrid Mignot
- Laboratoire d'Enzymologie et Biochimie Structurales, Centre de Recherche de Gif, CNRS, Bâtiment 34, 1 avenue de la Terrasse, 91198 Gif sur Yvette, France
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14
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Ranaivoson FM, Gigant B, Berritt S, Joullié M, Knossow M. Structural plasticity of tubulin assembly probed by vinca-domain ligands. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2012; 68:927-34. [DOI: 10.1107/s0907444912017143] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 04/18/2012] [Indexed: 11/10/2022]
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15
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Nawrotek A, Knossow M, Gigant B. The determinants that govern microtubule assembly from the atomic structure of GTP-tubulin. J Mol Biol 2011; 412:35-42. [PMID: 21787788 DOI: 10.1016/j.jmb.2011.07.029] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 07/13/2011] [Accepted: 07/14/2011] [Indexed: 10/18/2022]
Abstract
Tubulin alternates between a soluble curved structure and a microtubule straight conformation. GTP binding to αβ-tubulin is required for microtubule assembly, but whether this triggers conversion into a straighter structure is still debated. This is due, at least in part, to the lack of structural data for GTP-tubulin before assembly. Here, we report atomic-resolution crystal structures of soluble tubulin in the GDP and GTP nucleotide states in a complex with a stathmin-like domain. The structures differ locally in the neighborhood of the nucleotide. A loop movement in GTP-bound tubulin favors its recruitment to the ends of growing microtubules and facilitates its curved-to-straight transition, but this conversion has not proceeded yet. The data therefore argue for the conformational change toward the straight structure occurring as microtubule-specific contacts are established. They also suggest a model for the way the tubulin structure is modified in relation to microtubule assembly.
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Affiliation(s)
- Agata Nawrotek
- Laboratoire d'Enzymologie et Biochimie Structurales (LEBS), Centre de Recherche de Gif, CNRS, Bat. 34, 1, avenue de la Terrasse, 91198 Gif sur Yvette, France
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16
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Wu X, Shen QT, Oristian DS, Lu CP, Zheng Q, Wang HW, Fuchs E. Skin stem cells orchestrate directional migration by regulating microtubule-ACF7 connections through GSK3β. Cell 2011; 144:341-52. [PMID: 21295697 DOI: 10.1016/j.cell.2010.12.033] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Revised: 11/01/2010] [Accepted: 12/17/2010] [Indexed: 12/17/2022]
Abstract
Homeostasis and wound healing rely on stem cells (SCs) whose activity and directed migration are often governed by Wnt signaling. In dissecting how this pathway integrates with the necessary downstream cytoskeletal dynamics, we discovered that GSK3β, a kinase inhibited by Wnt signaling, directly phosphorylates ACF7, a > 500 kDa microtubule-actin crosslinking protein abundant in hair follicle stem cells (HF-SCs). We map ACF7's GSK3β sites to the microtubule-binding domain and show that phosphorylation uncouples ACF7 from microtubules. Phosphorylation-refractile ACF7 rescues overall microtubule architecture, but phosphorylation-constitutive mutants do not. Neither mutant rescues polarized movement, revealing that phospho-regulation must be dynamic. This circuitry is physiologically relevant and depends upon polarized GSK3β inhibition at the migrating front of SCs/progeny streaming from HFs during wound repair. Moreover, only ACF7 and not GSKβ-refractile-ACF7 restore polarized microtubule-growth and SC-migration to ACF7 null skin. Our findings provide insights into how this conserved spectraplakin integrates signaling, cytoskeletal dynamics, and polarized locomotion of somatic SCs.
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Affiliation(s)
- Xiaoyang Wu
- The Howard Hughes Medical Institute, Laboratory of Mammalian Cell Biology and Development, Rockefeller University, New York, NY 10065, USA
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17
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Duvernay MT, Wang H, Dong C, Guidry JJ, Sackett DL, Wu G. Alpha2B-adrenergic receptor interaction with tubulin controls its transport from the endoplasmic reticulum to the cell surface. J Biol Chem 2011; 286:14080-9. [PMID: 21357695 DOI: 10.1074/jbc.m111.222323] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
It is well recognized that the C terminus (CT) plays a crucial role in modulating G protein-coupled receptor (GPCR) transport from the endoplasmic reticulum (ER) to the cell surface. However the molecular mechanisms that govern CT-dependent ER export remain elusive. To address this issue, we used α(2B)-adrenergic receptor (α(2B)-AR) as a model GPCR to search for proteins interacting with the CT. By using peptide-conjugated affinity matrix combined with proteomics and glutathione S-transferase fusion protein pull-down assays, we identified tubulin directly interacting with the α(2B)-AR CT. The interaction domains were mapped to the acidic CT of tubulin and the basic Arg residues in the α(2B)-AR CT, particularly Arg-437, Arg-441, and Arg-446. More importantly, mutation of these Arg residues to disrupt tubulin interaction markedly inhibited α(2B)-AR transport to the cell surface and strongly arrested the receptor in the ER. These data provide the first evidence indicating that the α(2B)-AR C-terminal Arg cluster mediates its association with tubulin to coordinate its ER-to-cell surface traffic and suggest a novel mechanism of GPCR export through physical contact with microtubules.
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Affiliation(s)
- Matthew T Duvernay
- From the Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112
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18
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Lefèvre J, Chernov KG, Joshi V, Delga S, Toma F, Pastré D, Curmi PA, Savarin P. The C terminus of tubulin, a versatile partner for cationic molecules: binding of Tau, polyamines, and calcium. J Biol Chem 2010; 286:3065-78. [PMID: 21062741 DOI: 10.1074/jbc.m110.144089] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The C-terminal region of tubulin is involved in multiple aspects of the regulation of microtubule assembly. To elucidate the molecular mechanisms of this regulation, we study here, using different approaches, the interaction of Tau, spermine, and calcium, three representative partners of the tubulin C-terminal region, with a peptide composed of the last 42 residues of α1a-tubulin. The results show that their binding involves overlapping amino acid stretches in the C-terminal tubulin region: amino acid residues 421-441 for Tau, 430-432 and 444-451 for spermine, and 421-443 for calcium. Isothermal titration calorimetry, NMR, and cosedimentation experiments show that Tau and spermine have similar micromolar binding affinities, whereas their binding stoichiometry differs (C-terminal tubulin peptide/spermine stoichiometry 1:2, and C-terminal tubulin peptide/Tau stoichiometry 8:1). Interestingly, calcium, known as a negative regulator of microtubule assembly, can compete with the binding of Tau and spermine with the C-terminal domain of tubulin and with the positive effect of these two partners on microtubule assembly in vitro. This observation opens up the possibility that calcium may participate in the regulation of microtubule assembly in vivo through direct (still unknown) or indirect mechanism (displacement of microtubule partners). The functional importance of this part of tubulin was also underlined by the observation that an α-tubulin mutant deleted from the last 23 amino acid residues does not incorporate properly into the microtubule network of HeLa cells. Together, these results provide a structural basis for a better understanding of the complex interactions and putative competition of tubulin cationic partners with the C-terminal region of tubulin.
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Affiliation(s)
- Julien Lefèvre
- Laboratoire Structure-Activité des Biomolécules Normales et Pathologiques, INSERM-Université d'Evry-Val d'Essonne U829, Université Evry-Val d'Essonne, 91025 Evry, France
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19
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Banerjee A, Bovenzi FA, Bane SL. High-resolution separation of tubulin monomers on polyacrylamide minigels. Anal Biochem 2010; 402:194-6. [PMID: 20361920 DOI: 10.1016/j.ab.2010.03.035] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2010] [Revised: 03/18/2010] [Accepted: 03/29/2010] [Indexed: 10/19/2022]
Abstract
High-resolution separation of alpha- and beta-tubulin by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) on minigels can be performed rapidly using simple modifications of the standard Laemmli procedure. Separation of the subunits can be observed even in high-protein loads (up to 40microg of protein).
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20
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Gupta KK, Joyce MV, Slabbekoorn AR, Zhu ZC, Paulson BA, Boggess B, Goodson HV. Probing interactions between CLIP-170, EB1, and microtubules. J Mol Biol 2009; 395:1049-62. [PMID: 19913027 DOI: 10.1016/j.jmb.2009.11.014] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2009] [Revised: 11/03/2009] [Accepted: 11/05/2009] [Indexed: 10/20/2022]
Abstract
Cytoplasmic linker protein 170 (CLIP-170) is a microtubule (MT) plus-end tracking protein (+TIP) that dynamically localizes to the MT plus end and regulates MT dynamics. The mechanisms of these activities remain unclear because the CLIP-170-MT interaction is poorly understood, and even less is known about how CLIP-170 and other +TIPs act together as a network. CLIP-170 binds to the acidic C-terminal tail of alpha-tubulin. However, the observation that CLIP-170 has two CAP-Gly (cytoskeleton-associated protein glycine-rich) motifs and multiple serine-rich regions suggests that a single CLIP-170 molecule has multiple tubulin binding sites, and that these sites might bind to multiple parts of the tubulin dimer. Using a combination of chemical cross-linking and mass spectrometry, we find that CLIP-170 binds to both alpha-tubulin and beta-tubulin, and that binding is not limited to the acidic C-terminal tails. We provide evidence that these additional binding sites include the H12 helices of both alpha-tubulin and beta-tubulin and are significant for CLIP-170 activity. Previous work has shown that CLIP-170 binds to end-binding protein 1 (EB1) via the EB1 C-terminus, which mimics the acidic C-terminal tail of tubulin. We find that CLIP-170 can utilize its multiple tubulin binding sites to bind to EB1 and MT simultaneously. These observations help to explain how CLIP-170 can nucleate MTs and alter MT dynamics, and they contribute to understanding the significance and properties of the +TIP network.
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Affiliation(s)
- Kamlesh K Gupta
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
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21
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Hyperglutamylation of tubulin can either stabilize or destabilize microtubules in the same cell. EUKARYOTIC CELL 2009; 9:184-93. [PMID: 19700636 DOI: 10.1128/ec.00176-09] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In most eukaryotic cells, tubulin is subjected to posttranslational glutamylation, a conserved modification of unclear function. The glutamyl side chains form as branches of the primary sequence glutamic acids in two biochemically distinct steps: initiation and elongation. The length of the glutamyl side chain is spatially controlled and microtubule type specific. Here, we probe the significance of the glutamyl side chain length regulation in vivo by overexpressing a potent side chain elongase enzyme, Ttll6Ap, in Tetrahymena. Overexpression of Ttll6Ap caused hyperelongation of glutamyl side chains on the tubulin of axonemal, cortical, and cytoplasmic microtubules. Strikingly, in the same cell, hyperelongation of glutamyl side chains stabilized cytoplasmic microtubules and destabilized axonemal microtubules. Our observations suggest that the cellular outcomes of glutamylation are mediated by spatially restricted tubulin interactors of diverse nature.
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22
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Kumar P, Lyle KS, Gierke S, Matov A, Danuser G, Wittmann T. GSK3beta phosphorylation modulates CLASP-microtubule association and lamella microtubule attachment. ACTA ACUST UNITED AC 2009; 184:895-908. [PMID: 19289791 PMCID: PMC2699158 DOI: 10.1083/jcb.200901042] [Citation(s) in RCA: 143] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Polarity of the microtubule (MT) cytoskeleton is essential for many cell functions. Cytoplasmic linker–associated proteins (CLASPs) are MT-associated proteins thought to organize intracellular MTs and display a unique spatiotemporal regulation. In migrating epithelial cells, CLASPs track MT plus ends in the cell body but bind along MTs in the lamella. In this study, we demonstrate that glycogen synthase kinase 3β (GSK3β) directly phosphorylates CLASPs at multiple sites in the domain required for MT plus end tracking. Although complete phosphorylation disrupts both plus end tracking and association along lamella MTs, we show that partial phosphorylation of the identified GSK3β motifs determines whether CLASPs track plus ends or associate along MTs. In addition, we find that expression of constitutively active GSK3β destabilizes lamella MTs by disrupting lateral MT interactions with the cell cortex. GSK3β-induced lamella MT destabilization was partially rescued by expression of CLASP2 with mutated phosphorylation sites. This indicates that CLASP-mediated stabilization of peripheral MTs, which likely occurs in the vicinity of focal adhesions, may be regulated by local GSK3β inactivation.
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Affiliation(s)
- Praveen Kumar
- Department of Cell and Tissue Biology, University of California-San Francisco, San Francisco, CA 94143, USA
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23
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Miller SA, Johnson ML, Stukenberg PT. Kinetochore attachments require an interaction between unstructured tails on microtubules and Ndc80(Hec1). Curr Biol 2009; 18:1785-91. [PMID: 19026542 DOI: 10.1016/j.cub.2008.11.007] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2008] [Revised: 11/03/2008] [Accepted: 11/04/2008] [Indexed: 11/18/2022]
Abstract
Kinetochore attachments to microtubules are tight enough to move chromosomes, yet the microtubules' plus ends must remain dynamic and reposition within the attachment pocket during depolymerization-coupled movement. Kinetochores are unable to bind microtubules after any of the four subunits of the Ndc80 complex are knocked down [2, 4]; however, because the Ndc80 complex has important structural roles [1-3], it is unclear whether it directly mediates kinetochore-microtubule attachments. The Ndc80(Hec1) subunit (Hec1) has a microtubule-binding site composed of both an unstructured N-terminal tail and a calponin homology domain [5-7]. Here, we show that, surprisingly, the N-terminal tail is sufficient for microtubule-binding affinity in vitro. The interaction is salt sensitive, and the positively charged Hec1 tail cannot bind microtubules lacking negatively charged tails. We have replaced the endogenous Hec1 subunit with a mutant lacking the N-terminal tail. These cells assemble kinetochores properly but are unable to congress chromosomes, generate tension across sister kinetochores, or establish cold-stable kinetochore-microtubule attachments. Our data argue that the highest affinity interactions between kinetochores and microtubules are ionic attractions between two unstructured domains. We discuss the importance of this finding for models of repositioning of microtubules in the kinetochore during depolymerization.
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Affiliation(s)
- Stephanie A Miller
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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24
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Mechulam A, Chernov KG, Mucher E, Hamon L, Curmi PA, Pastré D. Polyamine sharing between tubulin dimers favours microtubule nucleation and elongation via facilitated diffusion. PLoS Comput Biol 2009; 5:e1000255. [PMID: 19119409 PMCID: PMC2599886 DOI: 10.1371/journal.pcbi.1000255] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2008] [Accepted: 11/17/2008] [Indexed: 12/18/2022] Open
Abstract
We suggest for the first time that the action of multivalent cations on microtubule dynamics can result from facilitated diffusion of GTP-tubulin to the microtubule ends. Facilitated diffusion can promote microtubule assembly, because, upon encountering a growing nucleus or the microtubule wall, random GTP-tubulin sliding on their surfaces will increase the probability of association to the target sites (nucleation sites or MT ends). This is an original explanation for understanding the apparent discrepancy between the high rate of microtubule elongation and the low rate of tubulin association at the microtubule ends in the viscous cytoplasm. The mechanism of facilitated diffusion requires an attraction force between two tubulins, which can result from the sharing of multivalent counterions. Natural polyamines (putrescine, spermidine, and spermine) are present in all living cells and are potent agents to trigger tubulin self-attraction. By using an analytical model, we analyze the implication of facilitated diffusion mediated by polyamines on nucleation and elongation of microtubules. In vitro experiments using pure tubulin indicate that the promotion of microtubule assembly by polyamines is typical of facilitated diffusion. The results presented here show that polyamines can be of particular importance for the regulation of the microtubule network in vivo and provide the basis for further investigations into the effects of facilitated diffusion on cytoskeleton dynamics.
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Affiliation(s)
- Alain Mechulam
- Laboratoire Structure-Activité des Biomolécules
Normales et Pathologiques, Université Evry-Val d'Essonne,
Evry, France
- INSERM, U829, Evry, France
| | - Konstantin G. Chernov
- Laboratoire Structure-Activité des Biomolécules
Normales et Pathologiques, Université Evry-Val d'Essonne,
Evry, France
- INSERM, U829, Evry, France
- Institute of Protein Research, Russian Academy of Sciences, Pushchino,
Moscow Region, Russia
| | - Elodie Mucher
- Laboratoire Structure-Activité des Biomolécules
Normales et Pathologiques, Université Evry-Val d'Essonne,
Evry, France
- INSERM, U829, Evry, France
| | - Loic Hamon
- Laboratoire Structure-Activité des Biomolécules
Normales et Pathologiques, Université Evry-Val d'Essonne,
Evry, France
- INSERM, U829, Evry, France
| | - Patrick A. Curmi
- Laboratoire Structure-Activité des Biomolécules
Normales et Pathologiques, Université Evry-Val d'Essonne,
Evry, France
- INSERM, U829, Evry, France
| | - David Pastré
- Laboratoire Structure-Activité des Biomolécules
Normales et Pathologiques, Université Evry-Val d'Essonne,
Evry, France
- INSERM, U829, Evry, France
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25
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Tubulin binding blocks mitochondrial voltage-dependent anion channel and regulates respiration. Proc Natl Acad Sci U S A 2008; 105:18746-51. [PMID: 19033201 DOI: 10.1073/pnas.0806303105] [Citation(s) in RCA: 286] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Regulation of mitochondrial outer membrane (MOM) permeability has dual importance: in normal metabolite and energy exchange between mitochondria and cytoplasm and thus in control of respiration, and in apoptosis by release of apoptogenic factors into the cytosol. However, the mechanism of this regulation, dependent on the voltage-dependent anion channel (VDAC), the major channel of MOM, remains controversial. A long-standing puzzle is that in permeabilized cells, adenine nucleotide translocase (ANT) is less accessible to cytosolic ADP than in isolated mitochondria. We solve this puzzle by finding a missing player in the regulation of MOM permeability: the cytoskeletal protein tubulin. We show that nanomolar concentrations of dimeric tubulin induce voltage-sensitive reversible closure of VDAC reconstituted into planar phospholipid membranes. Tubulin strikingly increases VDAC voltage sensitivity and at physiological salt conditions could induce VDAC closure at <10 mV transmembrane potentials. Experiments with isolated mitochondria confirm these findings. Tubulin added to isolated mitochondria decreases ADP availability to ANT, partially restoring the low MOM permeability (high apparent K(m) for ADP) found in permeabilized cells. Our findings suggest a previously unknown mechanism of regulation of mitochondrial energetics, governed by VDAC and tubulin at the mitochondria-cytosol interface. This tubulin-VDAC interaction requires tubulin anionic C-terminal tail (CTT) peptides. The significance of this interaction may be reflected in the evolutionary conservation of length and anionic charge in CTT throughout eukaryotes, despite wide changes in the exact sequence. Additionally, tubulins that have lost significant length or anionic character are only found in cells that do not have mitochondria.
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Chernov KG, Mechulam A, Popova NV, Pastre D, Nadezhdina ES, Skabkina OV, Shanina NA, Vasiliev VD, Tarrade A, Melki J, Joshi V, Baconnais S, Toma F, Ovchinnikov LP, Curmi PA. YB-1 promotes microtubule assembly in vitro through interaction with tubulin and microtubules. BMC BIOCHEMISTRY 2008; 9:23. [PMID: 18793384 PMCID: PMC2557009 DOI: 10.1186/1471-2091-9-23] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Accepted: 09/15/2008] [Indexed: 11/16/2022]
Abstract
Background YB-1 is a major regulator of gene expression in eukaryotic cells. In addition to its role in transcription, YB-1 plays a key role in translation and stabilization of mRNAs. Results We show here that YB-1 interacts with tubulin and microtubules and stimulates microtubule assembly in vitro. High resolution imaging via electron and atomic force microscopy revealed that microtubules assembled in the presence of YB-1 exhibited a normal single wall ultrastructure and indicated that YB-1 most probably coats the outer microtubule wall. Furthermore, we found that YB-1 also promotes the assembly of MAPs-tubulin and subtilisin-treated tubulin. Finally, we demonstrated that tubulin interferes with RNA:YB-1 complexes. Conclusion These results suggest that YB-1 may regulate microtubule assembly in vivo and that its interaction with tubulin may contribute to the control of mRNA translation.
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Affiliation(s)
- Konstantin G Chernov
- Laboratoire Structure-Activité des Biomolécules Normales et Pathologiques, INSERM/UEVE U829 Evry, 91025 France.
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27
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Conformational analysis of the carboxy-terminal tails of human beta-tubulin isotypes. Biophys J 2007; 94:1971-82. [PMID: 17993481 DOI: 10.1529/biophysj.107.115113] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Several isotypes of the structural protein tubulin have been characterized. Their expression offers a plausible explanation for differences regarding microtubule function. Although sequence variation between tubulin isotypes occurs throughout the entire protein, it is the extreme carboxy-terminal tails (CTTs) that exhibit the greatest concentration of differences. In humans, the CTTs range in length from 9 to 25 residues and because of a considerable number of glutamic acid residues, contain over 1/3 of tubulin's total electrostatic charge. The CTTs are believed to be highly disordered and their precise function has yet to be determined. However, their absence has been shown to result in altered microtubule stability and a reduction in the interaction with several microtubule-associated proteins (MAPs). To characterize the role that CTTs play in microtubule function, we examined the global conformational differences within a set of nine human beta-tubulin isotypes using replica exchange molecular dynamics simulations. Through the analysis of the resulting configuration ensembles, we quantified differences such as the CTTs sequence influence on overall flexibility and average secondary structure. Although only minor variations between each CTT were observed, we suggest that these differences may be significant enough to affect interactions with MAPs, thereby influencing important properties such as microtubule assembly and stability.
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Knipling L, Wolff J. Direct interaction of Bcl-2 proteins with tubulin. Biochem Biophys Res Commun 2006; 341:433-9. [PMID: 16446153 DOI: 10.1016/j.bbrc.2005.12.201] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2005] [Accepted: 12/31/2005] [Indexed: 11/24/2022]
Abstract
A direct interaction between tubulin and several pro-apoptotic and anti-apoptotic members of the Bcl-2 family has been demonstrated by effects on the assembly of microtubules from pure rat brain tubulin. Bcl-2, Bid, and Bad inhibit assembly sub-stoichiometrically, whereas peptides from Bak and Bax promote tubulin polymerization at near stoichiometric concentrations. These opposite effects on microtubule assembly are mutually antagonistic. The BH3 homology domains, common to all members of the family, are involved in the interaction with tubulin but do not themselves affect polymerization. Pelleting experiments with paclitaxel-stabilized microtubules show that Bak is associated with the microtubule pellet, whereas Bid remains primarily with the unpolymerized fraction. These interactions require the presence of the anionic C-termini of alpha- and beta-tubulin as they do not occur with tubulin S in which the C-termini have been removed. While in no way ruling out other pathways, such direct associations are the simplest potential regulatory mechanism for apoptosis resulting from disturbances in microtubule or tubulin function.
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Affiliation(s)
- Leslie Knipling
- Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
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29
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Zambito AM, Knipling L, Wolff J. Charge variants of tubulin, tubulin S, membrane-bound and palmitoylated tubulin from brain and pheochromocytoma cells. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1601:200-7. [PMID: 12445483 DOI: 10.1016/s1570-9639(02)00472-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Isoelectric focusing (IEF) of only approximately 1 microg of rat brain tubulin yields 27-30 distinct charge variants in the pH range of 4.5-5.4 with band separations of 0.01-0.02 pH units as detected by silver staining. Variants can be efficiently transferred from the immobilized gradient strip to polyvinylidene difluoride (PVDF) membranes for reaction with monoclonal antibodies. C-terminal-directed antibodies to alpha- and beta-tubulin yield patterns similar to N-terminal-directed antibodies. Removal of the acidic C-termini with subtilisin to form tubulin S increases the pI values by approximately 1 pH unit, leads to a loss in the isoelectric distinction between the alpha- and beta-tubulin variants seen by N-terminal-directed antibodies, and abolishes reactions with all beta-variants and all but three alpha variants by C-terminal-directed antibodies (TU-04 and TU-14). Many, but not all, of the variants are substrates for autopalmitoylation of rat brain tubulin. The distribution of isoelectric variants differs between cytoplasm and membrane fractions from PC12 pheochromocytoma cells. A potential role for different variants is suggested.
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Affiliation(s)
- Anna Maria Zambito
- Laboratory of Biochemistry and Genetics, NIDDK, NIH, Building 8, Room 2A23, 9000 Rockville Pike, Bethesda, MD 20892, USA
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Britto PJ, Knipling L, Wolff J. The local electrostatic environment determines cysteine reactivity of tubulin. J Biol Chem 2002; 277:29018-27. [PMID: 12023292 DOI: 10.1074/jbc.m204263200] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Of the 20 cysteines of rat brain tubulin, some react rapidly with sulfhydryl reagents, and some react slowly. The fast reacting cysteines cannot be distinguished with [14C]iodoacetamide, N-[(14)C]ethylmaleimide, or IAEDANS ([5-((((2-iodoacetyl)amino)ethyl)amino) naphthalene-1-sulfonic acid]), since modification to mole ratios 1 cysteine/dimer always leads to labeling of 6-7 cysteine residues. These have been identified as Cys-305alpha, Cys-315alpha, Cys-316alpha, Cys-347alpha, Cys-376alpha, Cys-241beta, and Cys-356beta by mass spectroscopy and sequencing. This lack of specificity can be ascribed to reagents that are too reactive; only with the relatively inactive chloroacetamide could we identify Cys-347alpha as the most reactive cysteine of tubulin. Using the 3.5-A electron diffraction structure, it could be shown that the reactive cysteines were within 6.5 A of positively charged arginines and lysines or the positive edges of aromatic rings, presumably promoting dissociation of the thiol to the thiolate anion. By the same reasoning the inactivity of a number of less reactive cysteines could be ascribed to inhibition of modification by negatively charged local environments, even with some surface-exposed cysteines. We conclude that the local electrostatic environment of cysteine is an important, although not necessarily the only, determinant of its reactivity.
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Affiliation(s)
- P J Britto
- Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA
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Watts NR, Sackett DL, Ward RD, Miller MW, Wingfield PT, Stahl SS, Steven AC. HIV-1 rev depolymerizes microtubules to form stable bilayered rings. J Cell Biol 2000; 150:349-60. [PMID: 10908577 PMCID: PMC2180222 DOI: 10.1083/jcb.150.2.349] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We describe a novel interaction between HIV-1 Rev and microtubules (MTs) that results in the formation of bilayered rings that are 44-49 nm in external diameter, 3.4-4.2 MD (megadaltons) in mass, and have 28-, 30-, or 32-fold symmetry. Ring formation is not sensitive to taxol, colchicine, or microtubule-associated proteins, but requires Mg(2+) and is inhibited by maytansine. The interaction involves the NH(2)-terminal domain of Rev and the face of tubulin exposed on the exterior of the MTs. The NH(2)-terminal half of Rev has unexpected sequence similarity to the tubulin-binding portion of the catalytic/motor domains of the microtubule-destabilizing Kin I kinesins. We propose a model wherein binding of Rev dimers to MTs at their ends causes segments of two neighboring protofilaments to peel off and close into rings, circumferentially containing 14, 15, or 16 tubulin heterodimers, with Rev bound on the inside. Rev has a strong inhibitory effect on aster formation in Xenopus egg extracts, demonstrating that it can interact with tubulin in the presence of normal levels of cellular constituents. These results suggest that Rev may interact with MTs to induce their destabilization, a proposition consistent with the previously described disruption of MTs after HIV-1 infection.
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Affiliation(s)
- Norman R. Watts
- Laboratory of Structural Biology Research, National Institute of Arthritis and Musculoskeletal and Skin Diseases
- Protein Expression Laboratory, National Institute of Arthritis and Musculoskeletal and Skin Diseases
| | - Dan L. Sackett
- Laboratory of Integrative and Medical Biophysics, National Institute of Child Health and Human Development
| | - Rita D. Ward
- Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Mill W. Miller
- Department of Biological Sciences, Wright State University, Dayton, Ohio 45435
| | - Paul T. Wingfield
- Protein Expression Laboratory, National Institute of Arthritis and Musculoskeletal and Skin Diseases
| | - Stephen S. Stahl
- Protein Expression Laboratory, National Institute of Arthritis and Musculoskeletal and Skin Diseases
| | - Alasdair C. Steven
- Laboratory of Structural Biology Research, National Institute of Arthritis and Musculoskeletal and Skin Diseases
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Abstract
Pure rat brain tubulin is readily palmitoylated in vitro using [3H]palmitoyl CoA but no added enzymes. A maximum of approximately six palmitic acids are added per dimer in 2-3 h at 36-37 degrees C under native conditions. Both alpha and beta tubulin are labeled, and 63-73% of the label was hydroxylamine-labile, presumed thioesters. Labeling increases with increasing pH and temperature, and with low concentrations of guanidine HCl or KCl (but not with urea) to a maximum of approximately 13 palmitates/dimer. High SDS and guanidine HCl concentrations are inhibitory. At no time could all 20 cysteine residues of the dimer be palmitoylated. Polymerization to microtubules, or use of tubulin S, markedly decreases the accessibility of the palmitoylation sites. Palmitoylation increases the electrophoretic mobility of a portion of alpha tubulin toward the beta band. Palmitoylated tubulin binds a colchicine analogue normally, but during three warm/cold polymerization/depolymerization cycles there is a progressive loss of palmitoylated tubulin, indicating decreased polymerization competence. We postulate that local electrostatic factors are major regulators of reactivity of tubulin cysteine residues toward palmitoyl CoA, and that the negative charges surrounding a number of the cysteines are sensitive to negative charges on palmitoyl CoA.
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Affiliation(s)
- J Wolff
- Laboratory of Biochemistry and Genetics, NIDDK, NIH, Bethesda, Maryland 20892, USA.
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