1
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Singh SK, Siegler N, Pandey H, Yanir N, Popov M, Goldstein-Levitin A, Sadan M, Debs G, Zarivach R, Frank GA, Kass I, Sindelar CV, Zalk R, Gheber L. Noncanonical interaction with microtubules via the N-terminal nonmotor domain is critical for the functions of a bidirectional kinesin. SCIENCE ADVANCES 2024; 10:eadi1367. [PMID: 38324691 PMCID: PMC10849588 DOI: 10.1126/sciadv.adi1367] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Accepted: 01/08/2024] [Indexed: 02/09/2024]
Abstract
Several kinesin-5 motors (kinesin-5s) exhibit bidirectional motility. The mechanism of such motility remains unknown. Bidirectional kinesin-5s share a long N-terminal nonmotor domain (NTnmd), absent in exclusively plus-end-directed kinesins. Here, we combined in vivo, in vitro, and cryo-electron microscopy (cryo-EM) studies to examine the impact of NTnmd mutations on the motor functions of the bidirectional kinesin-5, Cin8. We found that NTnmd deletion mutants exhibited cell viability and spindle localization defects. Using cryo-EM, we examined the structure of a microtubule (MT)-bound motor domain of Cin8, containing part of its NTnmd. Modeling and molecular dynamic simulations based on the cryo-EM map suggested that the NTnmd of Cin8 interacts with the C-terminal tail of β-tubulin. In vitro experiments on subtilisin-treated MTs confirmed this notion. Last, we showed that NTnmd mutants are defective in plus-end-directed motility in single-molecule and antiparallel MT sliding assays. These findings demonstrate that the NTnmd, common to bidirectional kinesin-5s, is critical for their bidirectional motility and intracellular functions.
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Affiliation(s)
- Sudhir K. Singh
- 1Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Nurit Siegler
- 1Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Himanshu Pandey
- 1Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Neta Yanir
- 1Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Mary Popov
- 1Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | | | - Mayan Sadan
- 1Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Garrett Debs
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06510, USA
| | - Raz Zarivach
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
- Ilse Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
- National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Gabriel A. Frank
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
- Ilse Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
- National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Itamar Kass
- Ilse Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Charles V. Sindelar
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06510, USA
| | - Ran Zalk
- Ilse Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Larisa Gheber
- 1Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
- Ilse Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
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2
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Muretta JM, Rajasekaran D, Blat Y, Little S, Myers M, Nair C, Burdekin B, Yuen SL, Jimenez N, Guhathakurta P, Wilson A, Thompson AR, Surti N, Connors D, Chase P, Harden D, Barbieri CM, Adam L, Thomas DD. HTS driven by fluorescence lifetime detection of FRET identifies activators and inhibitors of cardiac myosin. SLAS DISCOVERY : ADVANCING LIFE SCIENCES R & D 2023; 28:223-232. [PMID: 37307989 PMCID: PMC10422832 DOI: 10.1016/j.slasd.2023.06.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 05/08/2023] [Accepted: 06/07/2023] [Indexed: 06/14/2023]
Abstract
Small molecules that bind to allosteric sites on target proteins to alter protein function are highly sought in drug discovery. High-throughput screening (HTS) assays are needed to facilitate the direct discovery of allosterically active compounds. We have developed technology for high-throughput time-resolved fluorescence lifetime detection of fluorescence resonance energy transfer (FRET), which enables the detection of allosteric modulators by monitoring changes in protein structure. We tested this approach at the industrial scale by adapting an allosteric FRET sensor of cardiac myosin to high-throughput screening (HTS), based on technology provided by Photonic Pharma and the University of Minnesota, and then used the sensor to screen 1.6 million compounds in the HTS facility at Bristol Myers Squibb. The results identified allosteric activators and inhibitors of cardiac myosin that do not compete with ATP binding, demonstrating high potential for FLT-based drug discovery.
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Affiliation(s)
- J M Muretta
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America.
| | - D Rajasekaran
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - Y Blat
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - S Little
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - M Myers
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - C Nair
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - B Burdekin
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - S L Yuen
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - N Jimenez
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - P Guhathakurta
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - A Wilson
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - A R Thompson
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - N Surti
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - D Connors
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - P Chase
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - D Harden
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - C M Barbieri
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - L Adam
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - D D Thomas
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America.
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3
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Sladewski TE, Campbell PC, Billington N, D'Ordine A, Cole JL, de Graffenried CL. Cytokinesis in Trypanosoma brucei relies on an orphan kinesin that dynamically crosslinks microtubules. Curr Biol 2023; 33:899-911.e5. [PMID: 36787745 PMCID: PMC10023446 DOI: 10.1016/j.cub.2023.01.035] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 12/09/2022] [Accepted: 01/18/2023] [Indexed: 02/15/2023]
Abstract
Many single-celled eukaryotes have complex cell morphologies defined by microtubules arranged into higher-order structures. The auger-like shape of the parasitic protist Trypanosoma brucei (T. brucei) is mediated by a parallel array of microtubules that underlies the plasma membrane. The subpellicular array must be partitioned and segregated using a microtubule-based mechanism during cell division. We previously identified an orphan kinesin, KLIF, that localizes to the ingressing cleavage furrow and is essential for the completion of cytokinesis. We have characterized the biophysical properties of a truncated KLIF construct in vitro to gain mechanistic insight into the function of this novel kinesin. We find that KLIF is a non-processive dimeric kinesin that dynamically crosslinks microtubules. Microtubules crosslinked by KLIF in an antiparallel orientation are translocated relative to one another, while microtubules crosslinked parallel to one another remain static, resulting in the formation of organized parallel bundles. In addition, we find that KLIF stabilizes the alignment of microtubule plus ends. These features provide a mechanistic understanding for how KLIF functions to form a new pole of aligned microtubule plus ends that defines the shape of the new cell posterior, which is an essential requirement for the completion of cytokinesis in T. brucei.
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Affiliation(s)
- Thomas E Sladewski
- Department of Molecular Microbiology and Immunology, Brown University, Providence, RI 02912, USA; Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA.
| | - Paul C Campbell
- Department of Molecular Microbiology and Immunology, Brown University, Providence, RI 02912, USA
| | - Neil Billington
- Laboratory of Physiology, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda 20892, USA
| | - Alexandra D'Ordine
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, RI 02912, USA
| | - James L Cole
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA
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4
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Cardiac ryanodine receptor N-terminal region biosensors identify novel inhibitors via FRET-based high-throughput screening. J Biol Chem 2021; 298:101412. [PMID: 34793835 PMCID: PMC8689225 DOI: 10.1016/j.jbc.2021.101412] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Revised: 11/08/2021] [Accepted: 11/11/2021] [Indexed: 12/15/2022] Open
Abstract
The N-terminal region (NTR) of ryanodine receptor (RyR) channels is critical for the regulation of Ca2+ release during excitation–contraction (EC) coupling in muscle. The NTR hosts numerous mutations linked to skeletal (RyR1) and cardiac (RyR2) myopathies, highlighting its potential as a therapeutic target. Here, we constructed two biosensors by labeling the mouse RyR2 NTR at domains A, B, and C with FRET pairs. Using fluorescence lifetime (FLT) detection of intramolecular FRET signal, we developed high-throughput screening (HTS) assays with these biosensors to identify small-molecule RyR modulators. We then screened a small validation library and identified several hits. Hits with saturable FRET dose–response profiles and previously unreported effects on RyR were further tested using [3H]ryanodine binding to isolated sarcoplasmic reticulum vesicles to determine effects on intact RyR opening in its natural membrane. We identified three novel inhibitors of both RyR1 and RyR2 and two RyR1-selective inhibitors effective at nanomolar Ca2+. Two of these hits activated RyR1 only at micromolar Ca2+, highlighting them as potential enhancers of excitation–contraction coupling. To determine whether such hits can inhibit RyR leak in muscle, we further focused on one, an FDA-approved natural antibiotic, fusidic acid (FA). In skinned skeletal myofibers and permeabilized cardiomyocytes, FA inhibited RyR leak with no detrimental effect on skeletal myofiber excitation–contraction coupling. However, in intact cardiomyocytes, FA induced arrhythmogenic Ca2+ transients, a cautionary observation for a compound with an otherwise solid safety record. These results indicate that HTS campaigns using the NTR biosensor can identify compounds with therapeutic potential.
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5
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Goldstein-Levitin A, Pandey H, Allhuzaeel K, Kass I, Gheber L. Intracellular functions and motile properties of bi-directional kinesin-5 Cin8 are regulated by neck linker docking. eLife 2021; 10:71036. [PMID: 34387192 PMCID: PMC8456603 DOI: 10.7554/elife.71036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Accepted: 07/13/2021] [Indexed: 12/03/2022] Open
Abstract
In this study, we analyzed intracellular functions and motile properties of neck-linker (NL) variants of the bi-directional S. cerevisiae kinesin-5 motor, Cin8. We also examined – by modeling – the configuration of H-bonds during NL docking. Decreasing the number of stabilizing H-bonds resulted in partially functional variants, as long as a conserved backbone H-bond at the N-latch position (proposed to stabilize the docked conformation of the NL) remained intact. Elimination of this conserved H-bond resulted in production of a non-functional Cin8 variant. Surprisingly, additional H-bond stabilization of the N-latch position, generated by replacement of the NL of Cin8 by sequences of the plus-end directed kinesin-5 Eg5, also produced a nonfunctional variant. In that variant, a single replacement of N-latch asparagine with glycine, as present in Cin8, eliminated the additional H-bond stabilization and rescued the functional defects. We conclude that exact N-latch stabilization during NL docking is critical for the function of bi-directional kinesin-5 Cin8.
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Affiliation(s)
| | - Himanshu Pandey
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Kanary Allhuzaeel
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Itamar Kass
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel.,InterX LTD, Ramat-Gan, Israel
| | - Larisa Gheber
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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6
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Pandey H, Singh SK, Sadan M, Popov M, Singh M, Davidov G, Inagaki S, Al-Bassam J, Zarivach R, Rosenfeld SS, Gheber L. Flexible microtubule anchoring modulates the bi-directional motility of the kinesin-5 Cin8. Cell Mol Life Sci 2021; 78:6051-6068. [PMID: 34274977 PMCID: PMC11072411 DOI: 10.1007/s00018-021-03891-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 06/08/2021] [Accepted: 06/18/2021] [Indexed: 10/20/2022]
Abstract
Two modes of motility have been reported for bi-directional kinesin-5 motors: (a) context-dependent directionality reversal, a mode in which motors undergo persistent minus-end directed motility at the single-molecule level and switch to plus-end directed motility in different assays or under different conditions, such as during MT gliding or antiparallel sliding or as a function of motor clustering; and (b) bi-directional motility, defined as movement in two directions in the same assay, without persistent unidirectional motility. Here, we examine how modulation of motor-microtubule (MT) interactions affects these two modes of motility for the bi-directional kinesin-5, Cin8. We report that the large insert in loop 8 (L8) within the motor domain of Cin8 increases the MT affinity of Cin8 in vivo and in vitro and is required for Cin8 intracellular functions. We consistently found that recombinant purified L8 directly binds MTs and L8 induces single Cin8 motors to behave according to context-dependent directionality reversal and bi-directional motility modes at intermediate ionic strength and according to a bi-directional motility mode in an MT surface-gliding assay under low motor density conditions. We propose that the largely unstructured L8 facilitates flexible anchoring of Cin8 to the MTs. This flexible anchoring enables the direct observation of bi-directional motility in motility assays. Remarkably, although L8-deleted Cin8 variants exhibit a strong minus-end directed bias at the single-molecule level, they also exhibit plus-end directed motility in an MT-gliding assay. Thus, L8-induced flexible MT anchoring is required for bi-directional motility of single Cin8 molecules but is not necessary for context-dependent directionality reversal of Cin8 in an MT-gliding assay.
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Affiliation(s)
- Himanshu Pandey
- Department of Chemistry, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
- Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
| | - Sudhir Kumar Singh
- Department of Chemistry, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
| | - Mayan Sadan
- Department of Chemistry, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
| | - Mary Popov
- Department of Chemistry, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
| | - Meenakshi Singh
- Department of Chemistry, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
| | - Geula Davidov
- Department of Life Sciences and the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
| | - Sayaka Inagaki
- Department of Cancer Biology, Mayo Clinic, Jacksonville, FL, 32224, USA
| | - Jawdat Al-Bassam
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, 95616, USA
| | - Raz Zarivach
- Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
- Department of Life Sciences and the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel
| | | | - Larisa Gheber
- Department of Chemistry, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel.
- Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, 84105, Beer-Sheva, Israel.
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7
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Pandey H, Popov M, Goldstein-Levitin A, Gheber L. Mechanisms by Which Kinesin-5 Motors Perform Their Multiple Intracellular Functions. Int J Mol Sci 2021; 22:6420. [PMID: 34203964 PMCID: PMC8232732 DOI: 10.3390/ijms22126420] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Accepted: 06/07/2021] [Indexed: 11/16/2022] Open
Abstract
Bipolar kinesin-5 motor proteins perform multiple intracellular functions, mainly during mitotic cell division. Their specialized structural characteristics enable these motors to perform their essential functions by crosslinking and sliding apart antiparallel microtubules (MTs). In this review, we discuss the specialized structural features of kinesin-5 motors, and the mechanisms by which these features relate to kinesin-5 functions and motile properties. In addition, we discuss the multiple roles of the kinesin-5 motors in dividing as well as in non-dividing cells, and examine their roles in pathogenetic conditions. We describe the recently discovered bidirectional motility in fungi kinesin-5 motors, and discuss its possible physiological relevance. Finally, we also focus on the multiple mechanisms of regulation of these unique motor proteins.
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Affiliation(s)
| | | | | | - Larisa Gheber
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel; (H.P.); (M.P.); (A.G.-L.)
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8
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Pandey H, Reithmann E, Goldstein-Levitin A, Al-Bassam J, Frey E, Gheber L. Drag-induced directionality switching of kinesin-5 Cin8 revealed by cluster-motility analysis. SCIENCE ADVANCES 2021; 7:7/6/eabc1687. [PMID: 33547070 PMCID: PMC7864582 DOI: 10.1126/sciadv.abc1687] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Accepted: 12/18/2020] [Indexed: 05/29/2023]
Abstract
Directed active motion of motor proteins is a vital process in virtually all eukaryotic cells. Nearly a decade ago, the discovery of directionality switching of mitotic kinesin-5 motors challenged the long-standing paradigm that individual kinesin motors are characterized by an intrinsic directionality. The underlying mechanism, however, remains unexplained. Here, we studied clustering-induced directionality switching of the bidirectional kinesin-5 Cin8. Based on the characterization of single-molecule and cluster motility, we developed a model that predicts that directionality switching of Cin8 is caused by an asymmetric response of its active motion to opposing forces, referred to as drag. The model shows excellent quantitative agreement with experimental data obtained under high and low ionic strength conditions. Our analysis identifies a robust and general mechanism that explains why bidirectional motor proteins reverse direction in response to seemingly unrelated experimental factors including changes in motor density and molecular crowding, and in multimotor motility assays.
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Affiliation(s)
- Himanshu Pandey
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
| | - Emanuel Reithmann
- Arnold-Sommerfeld-Center for Theoretical Physics and Center for NanoScience, Ludwig-Maximilians-Universität München, Theresienstraße 37, D-80333 Munich, Germany
| | - Alina Goldstein-Levitin
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
| | - Jawdat Al-Bassam
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA
| | - Erwin Frey
- Arnold-Sommerfeld-Center for Theoretical Physics and Center for NanoScience, Ludwig-Maximilians-Universität München, Theresienstraße 37, D-80333 Munich, Germany.
| | - Larisa Gheber
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel.
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9
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Budaitis BG, Jariwala S, Rao L, Yue Y, Sept D, Verhey KJ, Gennerich A. Pathogenic mutations in the kinesin-3 motor KIF1A diminish force generation and movement through allosteric mechanisms. J Cell Biol 2021; 220:211720. [PMID: 33496723 PMCID: PMC7844421 DOI: 10.1083/jcb.202004227] [Citation(s) in RCA: 37] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 10/27/2020] [Accepted: 12/30/2020] [Indexed: 02/07/2023] Open
Abstract
The kinesin-3 motor KIF1A functions in neurons, where its fast and superprocessive motility facilitates long-distance transport, but little is known about its force-generating properties. Using optical tweezers, we demonstrate that KIF1A stalls at an opposing load of ~3 pN but more frequently detaches at lower forces. KIF1A rapidly reattaches to the microtubule to resume motion due to its class-specific K-loop, resulting in a unique clustering of force generation events. To test the importance of neck linker docking in KIF1A force generation, we introduced mutations linked to human neurodevelopmental disorders. Molecular dynamics simulations predict that V8M and Y89D mutations impair neck linker docking. Indeed, both mutations dramatically reduce the force generation of KIF1A but not the motor’s ability to rapidly reattach to the microtubule. Although both mutations relieve autoinhibition of the full-length motor, the mutant motors display decreased velocities, run lengths, and landing rates and delayed cargo transport in cells. These results advance our understanding of how mutations in KIF1A can manifest in disease.
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Affiliation(s)
- Breane G Budaitis
- Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI
| | - Shashank Jariwala
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI.,Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI
| | - Lu Rao
- Department of Anatomy and Structural Biology and Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, New York, NY
| | - Yang Yue
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI
| | - David Sept
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI
| | - Kristen J Verhey
- Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI.,Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI
| | - Arne Gennerich
- Department of Anatomy and Structural Biology and Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, New York, NY
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10
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How Kinesin-1 Utilize the Energy of Nucleotide: The Conformational Changes and Mechanochemical Coupling in the Unidirectional Motion of Kinesin-1. Int J Mol Sci 2020; 21:ijms21186977. [PMID: 32972035 PMCID: PMC7555842 DOI: 10.3390/ijms21186977] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Revised: 09/12/2020] [Accepted: 09/21/2020] [Indexed: 12/23/2022] Open
Abstract
Kinesin-1 is a typical motile molecular motor and the founding member of the kinesin family. The most significant feature in the unidirectional motion of kinesin-1 is its processivity. To realize the fast and processive movement on the microtubule lattice, kinesin-1 efficiently transforms the chemical energy of nucleotide binding and hydrolysis to the energy of mechanical movement. The chemical and mechanical cycle of kinesin-1 are coupled to avoid futile nucleotide hydrolysis. In this paper, the research on the mechanical pathway of energy transition and the regulating mechanism of the mechanochemical cycle of kinesin-1 is reviewed.
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11
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Zarrin A, Sivak DA, Brown AI. Breaking time-reversal symmetry for ratchet models of molecular machines. Phys Rev E 2019; 99:062127. [PMID: 31330673 DOI: 10.1103/physreve.99.062127] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Indexed: 06/10/2023]
Abstract
Biomolecular machines transduce free energy from one form to another to fulfill many important roles inside cells, with dissipation required to achieve directed progress. We investigate how to break time-reversal symmetry at a given dissipation cost by using deterministic protocols to drive systems over sawtooth potentials, which have frequently been used to model molecular machines as ratchets. Time asymmetry increases for sawtooth potentials with higher barriers and for driving potentials of intermediate width. For systems driven over a sawtooth potential according to a protocol, we find that symmetric sawtooths maximize time asymmetry, whereas earlier work examining ratchet models of molecular machines required asymmetric sawtooth potentials to achieve directed behavior. This distinction arises because deterministically driven machines are externally provided with direction, whereas autonomous machines must generate directed behavior.
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Affiliation(s)
- Arshia Zarrin
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A1S6, Canada
| | - David A Sivak
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A1S6, Canada
| | - Aidan I Brown
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A1S6, Canada
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
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12
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Budaitis BG, Jariwala S, Reinemann DN, Schimert KI, Scarabelli G, Grant BJ, Sept D, Lang MJ, Verhey KJ. Neck linker docking is critical for Kinesin-1 force generation in cells but at a cost to motor speed and processivity. eLife 2019; 8:44146. [PMID: 31084716 PMCID: PMC6533058 DOI: 10.7554/elife.44146] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 05/09/2019] [Indexed: 12/12/2022] Open
Abstract
Kinesin force generation involves ATP-induced docking of the neck linker (NL) along the motor core. However, the roles of the proposed steps of NL docking, cover-neck bundle (CNB) and asparagine latch (N-latch) formation, during force generation are unclear. Furthermore, the necessity of NL docking for transport of membrane-bound cargo in cells has not been tested. We generated kinesin-1 motors impaired in CNB and/or N-latch formation based on molecular dynamics simulations. The mutant motors displayed reduced force output and inability to stall in optical trap assays but exhibited increased speeds, run lengths, and landing rates under unloaded conditions. NL docking thus enhances force production but at a cost to speed and processivity. In cells, teams of mutant motors were hindered in their ability to drive transport of Golgi elements (high-load cargo) but not peroxisomes (low-load cargo). These results demonstrate that the NL serves as a mechanical element for kinesin-1 transport under physiological conditions.
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Affiliation(s)
- Breane G Budaitis
- Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, United States
| | - Shashank Jariwala
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, United States
| | - Dana N Reinemann
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, United States
| | | | - Guido Scarabelli
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, United States
| | - Barry J Grant
- Division of Biological Sciences, Section of Molecular Biology, University of California, San Diego, San Diego, United States
| | - David Sept
- Biophysics Program, University of Michigan, Ann Arbor, United States.,Department of Biomedical Engineering, University of Michigan, Ann Arbor, United States.,Center for Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, United States
| | - Matthew J Lang
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, United States.,Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, United States
| | - Kristen J Verhey
- Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, United States.,Biophysics Program, University of Michigan, Ann Arbor, United States.,Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, United States
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13
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Liang YJ, Yang WX. Kinesins in MAPK cascade: How kinesin motors are involved in the MAPK pathway? Gene 2019; 684:1-9. [DOI: 10.1016/j.gene.2018.10.042] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 09/27/2018] [Accepted: 10/16/2018] [Indexed: 12/12/2022]
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14
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Directionally biased sidestepping of Kip3/kinesin-8 is regulated by ATP waiting time and motor-microtubule interaction strength. Proc Natl Acad Sci U S A 2018; 115:E7950-E7959. [PMID: 30093386 DOI: 10.1073/pnas.1801820115] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Kinesin-8 motors, which move in a highly processive manner toward microtubule plus ends where they act as depolymerases, are essential regulators of microtubule dynamics in cells. To understand their navigation strategy on the microtubule lattice, we studied the 3D motion of single yeast kinesin-8 motors, Kip3, on freely suspended microtubules in vitro. We observed short-pitch, left-handed helical trajectories indicating that kinesin-8 motors frequently switch protofilaments in a directionally biased manner. Intriguingly, sidestepping was not directly coupled to forward stepping but rather depended on the average dwell time per forward step under limiting ATP concentrations. Based on our experimental findings and numerical simulations we propose that effective sidestepping toward the left is regulated by a bifurcation in the Kip3 step cycle, involving a transition from a two-head-bound to a one-head-bound conformation in the ATP-waiting state. Results from a kinesin-1 mutant with extended neck linker hint toward a generic sidestepping mechanism for processive kinesins, facilitating the circumvention of intracellular obstacles on the microtubule surface.
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15
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Liu M, Ran J, Zhou J. Non-canonical functions of the mitotic kinesin Eg5. Thorac Cancer 2018; 9:904-910. [PMID: 29927078 PMCID: PMC6068462 DOI: 10.1111/1759-7714.12792] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 05/24/2018] [Accepted: 05/24/2018] [Indexed: 01/25/2023] Open
Abstract
Kinesins are widely expressed, microtubule-dependent motors that play vital roles in microtubule-associated cellular activities, such as cell division and intracellular transport. Eg5, also known as kinesin-5 or kinesin spindle protein, is a member of the kinesin family that contributes to the formation and maintenance of the bipolar mitotic spindle during cell division. Small-molecule compounds that inhibit Eg5 activity have been shown to impair spindle assembly, block mitotic progression, and possess anti-cancer activity. Recent studies focusing on the localization and functions of Eg5 in plants have demonstrated that in addition to spindle organization, this motor protein has non-canonical functions, such as chromosome segregation and cytokinesis, that have not been observed in animals. In this review, we discuss the structure, function, and localization of Eg5 in various organisms, highlighting the specific role of this protein in plants. We also propose directions for the future studies of novel Eg5 functions based on the lessons learned from plants.
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Affiliation(s)
- Min Liu
- College of Life Sciences, Collaborative Innovation Center of Cell Biology in Universities of Shandong, Institute of Biomedical Sciences, Shandong Provincial Key Laboratory of Animal Resistance BiologyShandong Normal UniversityJinanChina
| | - Jie Ran
- College of Life Sciences, Collaborative Innovation Center of Cell Biology in Universities of Shandong, Institute of Biomedical Sciences, Shandong Provincial Key Laboratory of Animal Resistance BiologyShandong Normal UniversityJinanChina
| | - Jun Zhou
- College of Life Sciences, Collaborative Innovation Center of Cell Biology in Universities of Shandong, Institute of Biomedical Sciences, Shandong Provincial Key Laboratory of Animal Resistance BiologyShandong Normal UniversityJinanChina
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16
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Wu W, Jingbo S, Xu W, Liu J, Huang Y, Sheng Q, Lv Z. S-trityl-L-cysteine, a novel Eg5 inhibitor, is a potent chemotherapeutic strategy in neuroblastoma. Oncol Lett 2018; 16:1023-1030. [PMID: 29963178 DOI: 10.3892/ol.2018.8755] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 02/27/2018] [Indexed: 01/25/2023] Open
Abstract
Eg5 is a member of the kinesin-5 family. It is involved in the formation of the bipolar spindle and serves a crucial role in mitosis; meaning that mitotic activation may serve as a chemotherapeutic strategy. However, the anticancer activity of Eg5 inhibitors in neuroblastoma remains uncharacterized. In the present study, the expression of Eg5 was examined in clinical tissue samples and neuroblastoma cell lines, SK-N-SH, SH-SY5Y and SK-N-BE2. Additionally, the antitumor activity of the Eg5 inhibitor, S-trityl-L-cysteine (STLC), was confirmed in vitro. STLC could mediate cell apoptosis, as well as cell cycle arrest, in a dose-dependent manner, which may contribute toward its antitumor activity. STLC-mediated apoptosis and cell cycle arrest were triggered by activation of the mitogen-activated protein kinase and nuclear factor kB signaling pathways. These results suggested that STLC may have potential in the in vivo treatment of neuroblastoma.
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Affiliation(s)
- Wei Wu
- Department of General Surgery, Shanghai Children's Hospital, Shanghai Jiao Tong University, Shanghai 200062, P.R. China
| | - Shao Jingbo
- Department of Hematology, Shanghai Children's Hospital, Shanghai Jiao Tong University, Shanghai 200062, P.R. China
| | - Weijue Xu
- Department of General Surgery, Shanghai Children's Hospital, Shanghai Jiao Tong University, Shanghai 200062, P.R. China
| | - Jiangbin Liu
- Department of General Surgery, Shanghai Children's Hospital, Shanghai Jiao Tong University, Shanghai 200062, P.R. China
| | - Yiming Huang
- Department of General Surgery, Shanghai Children's Hospital, Shanghai Jiao Tong University, Shanghai 200062, P.R. China
| | - Qingfeng Sheng
- Department of General Surgery, Shanghai Children's Hospital, Shanghai Jiao Tong University, Shanghai 200062, P.R. China
| | - Zhibao Lv
- Department of General Surgery, Shanghai Children's Hospital, Shanghai Jiao Tong University, Shanghai 200062, P.R. China
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17
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Milic B, Chakraborty A, Han K, Bassik MC, Block SM. KIF15 nanomechanics and kinesin inhibitors, with implications for cancer chemotherapeutics. Proc Natl Acad Sci U S A 2018; 115:E4613-E4622. [PMID: 29703754 PMCID: PMC5960320 DOI: 10.1073/pnas.1801242115] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Eg5, a mitotic kinesin, has been a target for anticancer drug development. Clinical trials of small-molecule inhibitors of Eg5 have been stymied by the development of resistance, attributable to mitotic rescue by a different endogenous kinesin, KIF15. Compared with Eg5, relatively little is known about the properties of the KIF15 motor. Here, we employed single-molecule optical-trapping techniques to define the KIF15 mechanochemical cycle. We also studied the inhibitory effects of KIF15-IN-1, an uncharacterized, commercially available, small-molecule inhibitor, on KIF15 motility. To explore the complementary behaviors of KIF15 and Eg5, we also scored the effects of small-molecule inhibitors on admixtures of both motors, using both a microtubule (MT)-gliding assay and an assay for cancer cell viability. We found that (i) KIF15 motility differs significantly from Eg5; (ii) KIF15-IN-1 is a potent inhibitor of KIF15 motility; (iii) MT gliding powered by KIF15 and Eg5 only ceases when both motors are inhibited; and (iv) pairing KIF15-IN-1 with Eg5 inhibitors synergistically reduces cancer cell growth. Taken together, our results lend support to the notion that a combination drug therapy employing both inhibitors may be a viable strategy for overcoming chemotherapeutic resistance.
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Affiliation(s)
- Bojan Milic
- Biophysics Program, Stanford University, Stanford, CA 94305
| | | | - Kyuho Han
- Department of Genetics, Stanford University School of Medicine, Stanford University, Stanford, CA 94305
| | - Michael C Bassik
- Department of Genetics, Stanford University School of Medicine, Stanford University, Stanford, CA 94305
- Chemistry, Engineering, and Medicine for Human Health, Stanford University, Stanford, CA 94305
| | - Steven M Block
- Department of Biology, Stanford University, Stanford, CA 94305;
- Department of Applied Physics, Stanford University, Stanford, CA 94305
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18
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Singh SK, Pandey H, Al-Bassam J, Gheber L. Bidirectional motility of kinesin-5 motor proteins: structural determinants, cumulative functions and physiological roles. Cell Mol Life Sci 2018; 75:1757-1771. [PMID: 29397398 PMCID: PMC11105280 DOI: 10.1007/s00018-018-2754-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2017] [Revised: 01/03/2018] [Accepted: 01/17/2018] [Indexed: 01/27/2023]
Abstract
Mitotic kinesin-5 bipolar motor proteins perform essential functions in mitotic spindle dynamics by crosslinking and sliding antiparallel microtubules (MTs) apart within the mitotic spindle. Two recent studies have indicated that single molecules of Cin8, the Saccharomyces cerevisiae kinesin-5 homolog, are minus end-directed when moving on single MTs, yet switch directionality under certain experimental conditions (Gerson-Gurwitz et al., EMBO J 30:4942-4954, 2011; Roostalu et al., Science 332:94-99, 2011). This finding was unexpected since the Cin8 catalytic motor domain is located at the N-terminus of the protein, and such kinesins have been previously thought to be exclusively plus end-directed. In addition, the essential intracellular functions of kinesin-5 motors in separating spindle poles during mitosis can only be accomplished by plus end-directed motility during antiparallel sliding of the spindle MTs. Thus, the mechanism and possible physiological role of the minus end-directed motility of kinesin-5 motors remain unclear. Experimental and theoretical studies from several laboratories in recent years have identified additional kinesin-5 motors that are bidirectional, revealed structural determinants that regulate directionality, examined the possible mechanisms involved and have proposed physiological roles for the minus end-directed motility of kinesin-5 motors. Here, we summarize our current understanding of the remarkable ability of certain kinesin-5 motors to switch directionality when moving along MTs.
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Affiliation(s)
- Sudhir Kumar Singh
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, PO Box 653, 84105, Beer-Sheva, Israel
| | - Himanshu Pandey
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, PO Box 653, 84105, Beer-Sheva, Israel
| | - Jawdat Al-Bassam
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, 95616, USA
| | - Larisa Gheber
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, PO Box 653, 84105, Beer-Sheva, Israel.
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19
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A posttranslational modification of the mitotic kinesin Eg5 that enhances its mechanochemical coupling and alters its mitotic function. Proc Natl Acad Sci U S A 2018; 115:E1779-E1788. [PMID: 29432173 DOI: 10.1073/pnas.1718290115] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Numerous posttranslational modifications have been described in kinesins, but their consequences on motor mechanics are largely unknown. We investigated one of these-acetylation of lysine 146 in Eg5-by creating an acetylation mimetic lysine to glutamine substitution (K146Q). Lysine 146 is located in the α2 helix of the motor domain, where it makes an ionic bond with aspartate 91 on the neighboring α1 helix. Molecular dynamics simulations predict that disrupting this bond enhances catalytic site-neck linker coupling. We tested this using structural kinetics and single-molecule mechanics and found that the K146Q mutation increases motor performance under load and coupling of the neck linker to catalytic site. These changes convert Eg5 from a motor that dissociates from the microtubule at low load into one that is more tightly coupled and dissociation resistant-features shared by kinesin 1. These features combined with the increased propensity to stall predict that the K146Q Eg5 acetylation mimetic should act in the cell as a "brake" that slows spindle pole separation, and we have confirmed this by expressing this modified motor in mitotically active cells. Thus, our results illustrate how a posttranslational modification of a kinesin can be used to fine tune motor behavior to meet specific physiological needs.
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20
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Hwang W, Lang MJ, Karplus M. Kinesin motility is driven by subdomain dynamics. eLife 2017; 6:28948. [PMID: 29111975 PMCID: PMC5718755 DOI: 10.7554/elife.28948] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Accepted: 11/03/2017] [Indexed: 12/13/2022] Open
Abstract
The microtubule (MT)-associated motor protein kinesin utilizes its conserved ATPase head to achieve diverse motility characteristics. Despite considerable knowledge about how its ATPase activity and MT binding are coupled to the motility cycle, the atomic mechanism of the core events remain to be found. To obtain insights into the mechanism, we performed 38.5 microseconds of all-atom molecular dynamics simulations of kinesin-MT complexes in different nucleotide states. Local subdomain dynamics were found to be essential for nucleotide processing. Catalytic water molecules are dynamically organized by the switch domains of the nucleotide binding pocket while ATP is torsionally strained. Hydrolysis products are 'pulled' by switch-I, and a new ATP is 'captured' by a concerted motion of the α0/L5/switch-I trio. The dynamic and wet kinesin-MT interface is tuned for rapid interactions while maintaining specificity. The proposed mechanism provides the flexibility necessary for walking in the crowded cellular environment. Motor proteins called kinesins perform a number of different roles inside cells, including transporting cargo and organizing filaments called microtubules to generate the force needed for a cell to divide. Kinesins move along the microtubules, with different kinesins moving in different ways: some ‘walk’, some jump, and some destroy the microtubule as they travel along it. All kinesins power their movements using the same molecule as fuel – adenosine triphosphate, known as ATP for short. Energy stored in ATP is released by a chemical reaction known as hydrolysis, which uses water to break off specific parts of the ATP molecule. The site to which ATP binds in a kinesin has a similar structure to the ATP binding site of many other proteins that use ATP. However, little was known about the way in which kinesin uses ATP as a fuel, including how ATP binds to kinesin and is hydrolyzed, and how the products of hydrolysis are released. These events are used to power the motor protein. Hwang et al. have used powerful computer simulation methods to examine in detail how ATP interacts with kinesin whilst moving across a microtubule. The simulations suggest that regions (or 'domains') of kinesin near the ATP binding site move around to help in processing ATP. These kinesin domains trap a nearby ATP molecule from the environment and help to deliver water molecules to ATP for hydrolysis. Hwang et al. also found that the domain motion subsequently helps in the release of the hydrolysis products by kinesin. The domains around the ATP pocket vary among the kinesins and these differences may enable kinesins to fine-tune how they use ATP to move. Further investigations will help us understand why different kinesin families behave differently. They will also contribute to exploring how kinesin inhibitors might be used as anti-cancer drugs.
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Affiliation(s)
- Wonmuk Hwang
- Department of Biomedical Engineering, Texas A&M University, College Station, United States.,Department of Materials Science & Engineering, Texas A&M University, College Station, United States.,School of Computational Sciences, Korea Institute for Advanced Study, Seoul, Korea
| | - Matthew J Lang
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, United States.,Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, United States
| | - Martin Karplus
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, United States.,Laboratoire de Chimie Biophysique, ISIS, Université de Strasbourg, Strasbourg, France
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21
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Peulen TO, Opanasyuk O, Seidel CAM. Combining Graphical and Analytical Methods with Molecular Simulations To Analyze Time-Resolved FRET Measurements of Labeled Macromolecules Accurately. J Phys Chem B 2017; 121:8211-8241. [PMID: 28709377 PMCID: PMC5592652 DOI: 10.1021/acs.jpcb.7b03441] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
![]()
Förster resonance energy transfer
(FRET) measurements from
a donor, D, to an acceptor, A, fluorophore are frequently used in vitro and in live cells to reveal information on the
structure and dynamics of DA labeled macromolecules. Accurate descriptions
of FRET measurements by molecular models are complicated because the
fluorophores are usually coupled to the macromolecule via flexible
long linkers allowing for diffusional exchange between multiple states
with different fluorescence properties caused by distinct environmental
quenching, dye mobilities, and variable DA distances. It is often
assumed for the analysis of fluorescence intensity decays that DA
distances and D quenching are uncorrelated (homogeneous quenching
by FRET) and that the exchange between distinct fluorophore states
is slow (quasistatic). This allows us to introduce the FRET-induced
donor decay, εD(t), a function solely
depending on the species fraction distribution of the rate constants
of energy transfer by FRET, for a convenient joint analysis of fluorescence
decays of FRET and reference samples by integrated graphical and analytical
procedures. Additionally, we developed a simulation toolkit to model
dye diffusion, fluorescence quenching by the protein surface, and
FRET. A benchmark study with simulated fluorescence decays of 500
protein structures demonstrates that the quasistatic homogeneous model
works very well and recovers for single conformations the average
DA distances with an accuracy of < 2%. For more complex
cases, where proteins adopt multiple conformations with significantly
different dye environments (heterogeneous case), we introduce a general
analysis framework and evaluate its power in resolving heterogeneities
in DA distances. The developed fast simulation methods, relying on
Brownian dynamics of a coarse-grained dye in its sterically accessible
volume, allow us to incorporate structural information in the decay
analysis for heterogeneous cases by relating dye states with protein
conformations to pave the way for fluorescence and FRET-based dynamic
structural biology. Finally, we present theories and simulations to
assess the accuracy and precision of steady-state and time-resolved
FRET measurements in resolving DA distances on the single-molecule
and ensemble level and provide a rigorous framework for estimating
approximation, systematic, and statistical errors.
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Affiliation(s)
- Thomas-Otavio Peulen
- Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität , Universitätsstraße 1, 40225 Düsseldorf, Germany
| | - Oleg Opanasyuk
- Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität , Universitätsstraße 1, 40225 Düsseldorf, Germany
| | - Claus A M Seidel
- Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität , Universitätsstraße 1, 40225 Düsseldorf, Germany
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22
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Li L, Jia Z, Peng Y, Godar S, Getov I, Teng S, Alper J, Alexov E. Forces and Disease: Electrostatic force differences caused by mutations in kinesin motor domains can distinguish between disease-causing and non-disease-causing mutations. Sci Rep 2017; 7:8237. [PMID: 28811629 PMCID: PMC5557957 DOI: 10.1038/s41598-017-08419-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 07/10/2017] [Indexed: 01/09/2023] Open
Abstract
The ability to predict if a given mutation is disease-causing or not has enormous potential to impact human health. Typically, these predictions are made by assessing the effects of mutation on macromolecular stability and amino acid conservation. Here we report a novel feature: the electrostatic component of the force acting between a kinesin motor domain and tubulin. We demonstrate that changes in the electrostatic component of the binding force are able to discriminate between disease-causing and non-disease-causing mutations found in human kinesin motor domains using the receiver operating characteristic (ROC). Because diseases may originate from multiple effects not related to kinesin-microtubule binding, the prediction rate of 0.843 area under the ROC plot due to the change in magnitude of the electrostatic force alone is remarkable. These results reflect the dependence of kinesin’s function on motility along the microtubule, which suggests a precise balance of microtubule binding forces is required.
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Affiliation(s)
- Lin Li
- Department of Physics and Astronomy, Clemson University, Clemson, SC, 29634, USA
| | - Zhe Jia
- Department of Physics and Astronomy, Clemson University, Clemson, SC, 29634, USA
| | - Yunhui Peng
- Department of Physics and Astronomy, Clemson University, Clemson, SC, 29634, USA
| | - Subash Godar
- Department of Physics and Astronomy, Clemson University, Clemson, SC, 29634, USA
| | - Ivan Getov
- Department of Chemical Engineering, Clemson University, Clemson, SC, 29634, USA
| | - Shaolei Teng
- Department of Biology, Howard University, Washington, DC, 20059, USA
| | - Joshua Alper
- Department of Physics and Astronomy, Clemson University, Clemson, SC, 29634, USA.
| | - Emil Alexov
- Department of Physics and Astronomy, Clemson University, Clemson, SC, 29634, USA.
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23
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Intraflagellar transport velocity is governed by the number of active KIF17 and KIF3AB motors and their motility properties under load. Proc Natl Acad Sci U S A 2017; 114:E6830-E6838. [PMID: 28761002 DOI: 10.1073/pnas.1708157114] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Homodimeric KIF17 and heterotrimeric KIF3AB are processive, kinesin-2 family motors that act jointly to carry out anterograde intraflagellar transport (IFT), ferrying cargo along microtubules (MTs) toward the tips of cilia. How IFT trains attain speeds that exceed the unloaded rate of the slower, KIF3AB motor remains unknown. By characterizing the motility properties of kinesin-2 motors as a function of load we find that the increase in KIF3AB velocity, elicited by forward loads from KIF17 motors, cannot alone account for the speed of IFT trains in vivo. Instead, higher IFT velocities arise from an increased likelihood that KIF3AB motors dissociate from the MT, resulting in transport by KIF17 motors alone, unencumbered by opposition from KIF3AB. The rate of transport is therefore set by an equilibrium between a faster state, where only KIF17 motors move the train, and a slower state, where at least one KIF3AB motor on the train remains active in transport. The more frequently the faster state is accessed, the higher the overall velocity of the IFT train. We conclude that IFT velocity is governed by (i) the absolute numbers of each motor type on a given train, (ii) how prone KIF3AB is to dissociation from MTs relative to KIF17, and (iii) how prone both motors are to dissociation relative to binding MTs.
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24
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Bickel KG, Mann BJ, Waitzman JS, Poor TA, Rice SE, Wadsworth P. Src family kinase phosphorylation of the motor domain of the human kinesin-5, Eg5. Cytoskeleton (Hoboken) 2017. [PMID: 28646493 DOI: 10.1002/cm.21380] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Spindle formation in mammalian cells requires precise spatial and temporal regulation of the kinesin-5, Eg5, which generates outward force to establish spindle bipolarity. Our results demonstrate that Eg5 is phosphorylated in cultured cells by Src family kinases (SFKs) at three sites in the motor head: Y125, Y211, and Y231. Mutation of these sites diminishes motor activity in vitro, and replacement of endogenous Eg5 with phosphomimetic Y211 in LLC-Pk1 cells results in monopolar spindles, consistent with loss of Eg5 activity. Cells treated with SFK inhibitors show defects in spindle formation, similar to those in cells expressing the nonphosphorylatable Y211 mutant, and distinct from inhibition of other mitotic kinases. We propose that this phosphoregulatory mechanism tunes Eg5 enzymatic activity for optimal spindle morphology.
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Affiliation(s)
- Kathleen G Bickel
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, 60611
| | - Barbara J Mann
- Department of Biology, University of Massachusetts, Amherst, Massachusetts, 01003
| | - Joshua S Waitzman
- Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, 60611
| | - Taylor A Poor
- Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, 60611
| | - Sarah E Rice
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, 60611
| | - Patricia Wadsworth
- Department of Biology, University of Massachusetts, Amherst, Massachusetts, 01003
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25
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Bell KM, Cha HK, Sindelar CV, Cochran JC. The yeast kinesin-5 Cin8 interacts with the microtubule in a noncanonical manner. J Biol Chem 2017; 292:14680-14694. [PMID: 28701465 PMCID: PMC5582858 DOI: 10.1074/jbc.m117.797662] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Revised: 06/28/2017] [Indexed: 11/06/2022] Open
Abstract
Kinesin motors play central roles in establishing and maintaining the mitotic spindle during cell division. Unlike most other kinesins, Cin8, a kinesin-5 motor in Saccharomyces cerevisiae, can move bidirectionally along microtubules, switching directionality according to biochemical conditions, a behavior that remains largely unexplained. To this end, we used biochemical rate and equilibrium constant measurements as well as cryo-electron microscopy methodologies to investigate the microtubule interactions of the Cin8 motor domain. These experiments unexpectedly revealed that, whereas Cin8 ATPase kinetics fell within measured ranges for kinesins (especially kinesin-5 proteins), approximately four motors can bind each αβ-tubulin dimer within the microtubule lattice. This result contrasted with those observations on other known kinesins, which can bind only a single "canonical" site per tubulin dimer. Competition assays with human kinesin-5 (Eg5) only partially abrogated this behavior, indicating that Cin8 binds microtubules not only at the canonical site, but also one or more separate ("noncanonical") sites. Moreover, we found that deleting the large, class-specific insert in the microtubule-binding loop 8 reverts Cin8 to one motor per αβ-tubulin in the microtubule. The novel microtubule-binding mode of Cin8 identified here provides a potential explanation for Cin8 clustering along microtubules and potentially may contribute to the mechanism for direction reversal.
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Affiliation(s)
- Kayla M Bell
- From the Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405
| | - Hyo Keun Cha
- the Department of Cell Biology, Yale School of Medicine, and
| | - Charles V Sindelar
- the Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520
| | - Jared C Cochran
- From the Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405,
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26
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Chen GY, Kang YJ, Gayek AS, Youyen W, Tüzel E, Ohi R, Hancock WO. Eg5 Inhibitors Have Contrasting Effects on Microtubule Stability and Metaphase Spindle Integrity. ACS Chem Biol 2017; 12:1038-1046. [PMID: 28165699 DOI: 10.1021/acschembio.6b01040] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
To uncover their contrasting mechanisms, antimitotic drugs that inhibit Eg5 (kinesin-5) were analyzed in mixed-motor gliding assays of kinesin-1 and Eg5 motors in which Eg5 "braking" dominates motility. Loop-5 inhibitors (monastrol, STLC, ispinesib, and filanesib) increased gliding speeds, consistent with inducing a weak-binding state in Eg5, whereas BRD9876 slowed gliding, consistent with locking Eg5 in a rigor state. Biochemical and single-molecule assays demonstrated that BRD9876 acts as an ATP- and ADP-competitive inhibitor with 4 nM KI. Consistent with its microtubule polymerase activity, Eg5 was shown to stabilize microtubules against depolymerization. This stabilization activity was eliminated in monastrol but was enhanced by BRD9876. Finally, in metaphase-arrested RPE-1 cells, STLC promoted spindle collapse, whereas BRD9876 did not. Thus, different Eg5 inhibitors impact spindle assembly and architecture through contrasting mechanisms, and rigor inhibitors may paradoxically have the capacity to stabilize microtubule arrays in cells.
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Affiliation(s)
- Geng-Yuan Chen
- Department
of Biomedical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - You Jung Kang
- Department
of Biomedical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - A. Sophia Gayek
- Department
of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee 37203, United States
| | - Wiphu Youyen
- Department
of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States
| | - Erkan Tüzel
- Department
of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States
| | - Ryoma Ohi
- Department
of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee 37203, United States
| | - William O. Hancock
- Department
of Biomedical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
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27
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Schaaf TM, Peterson KC, Grant BD, Bawaskar P, Yuen S, Li J, Muretta JM, Gillispie GD, Thomas DD. High-Throughput Spectral and Lifetime-Based FRET Screening in Living Cells to Identify Small-Molecule Effectors of SERCA. SLAS DISCOVERY : ADVANCING LIFE SCIENCES R & D 2017; 22:262-273. [PMID: 27899691 PMCID: PMC5323330 DOI: 10.1177/1087057116680151] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
A robust high-throughput screening (HTS) strategy has been developed to discover small-molecule effectors targeting the sarco/endoplasmic reticulum calcium ATPase (SERCA), based on a fluorescence microplate reader that records both the nanosecond decay waveform (lifetime mode) and the complete emission spectrum (spectral mode), with high precision and speed. This spectral unmixing plate reader (SUPR) was used to screen libraries of small molecules with a fluorescence resonance energy transfer (FRET) biosensor expressed in living cells. Ligand binding was detected by FRET associated with structural rearrangements of green fluorescent protein (GFP, donor) and red fluorescent protein (RFP, acceptor) fused to the cardiac-specific SERCA2a isoform. The results demonstrate accurate quantitation of FRET along with high precision of hit identification. Fluorescence lifetime analysis resolved SERCA's distinct structural states, providing a method to classify small-molecule chemotypes on the basis of their structural effect on the target. The spectral analysis was also applied to flag interference by fluorescent compounds. FRET hits were further evaluated for functional effects on SERCA's ATPase activity via both a coupled-enzyme assay and a FRET-based calcium sensor. Concentration-response curves indicated excellent correlation between FRET and function. These complementary spectral and lifetime FRET detection methods offer an attractive combination of precision, speed, and resolution for HTS.
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Affiliation(s)
- Tory M. Schaaf
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | | | | | - Prachi Bawaskar
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Samantha Yuen
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Ji Li
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Joseph M. Muretta
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | | | - David D. Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
- Photonic Pharma LLC, Minneapolis, MN 55410
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28
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Heart failure drug changes the mechanoenzymology of the cardiac myosin powerstroke. Proc Natl Acad Sci U S A 2017; 114:E1796-E1804. [PMID: 28223517 DOI: 10.1073/pnas.1611698114] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Omecamtiv mecarbil (OM), a putative heart failure therapeutic, increases cardiac contractility. We hypothesize that it does this by changing the structural kinetics of the myosin powerstroke. We tested this directly by performing transient time-resolved FRET on a ventricular cardiac myosin biosensor. Our results demonstrate that OM stabilizes myosin's prepowerstroke structural state, supporting previous measurements showing that the drug shifts the equilibrium constant for myosin-catalyzed ATP hydrolysis toward the posthydrolysis biochemical state. OM slowed the actin-induced powerstroke, despite a twofold increase in the rate constant for actin-activated phosphate release, the biochemical step in myosin's ATPase cycle associated with force generation and the conversion of chemical energy into mechanical work. We conclude that OM alters the energetics of cardiac myosin's mechanical cycle, causing the powerstroke to occur after myosin weakly binds to actin and releases phosphate. We discuss the physiological implications for these changes.
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29
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Hancock WO. The Kinesin-1 Chemomechanical Cycle: Stepping Toward a Consensus. Biophys J 2016; 110:1216-25. [PMID: 27028632 DOI: 10.1016/j.bpj.2016.02.025] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Revised: 01/23/2016] [Accepted: 02/03/2016] [Indexed: 10/22/2022] Open
Abstract
Kinesin-1 serves as a model for understanding fundamentals of motor protein mechanochemistry and for interpreting functional diversity across the kinesin superfamily. Despite sustained work over the last three decades, disagreements remain regarding the events that trigger the two key transitions in the stepping cycle: detachment of the trailing head from the microtubule and binding of the tethered head to the next tubulin binding site. This review describes the conflicting views of these events and highlights recent work that sheds light on these long-standing controversies. It concludes by presenting a consensus kinesin-1 chemomechanical that incorporates recent work, resolves discrepancies, and highlights key questions for future experimental work. It is hoped that this model provides a framework for understanding how diverse kinesins are tuned for their specific cellular roles.
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Affiliation(s)
- William O Hancock
- Department of Biomedical Engineering, Pennsylvania State University, University Park, Pennsylvania.
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30
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Brown AI, Sivak DA. Effective dissipation: Breaking time-reversal symmetry in driven microscopic energy transmission. Phys Rev E 2016; 94:032137. [PMID: 27739864 DOI: 10.1103/physreve.94.032137] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Indexed: 06/06/2023]
Abstract
At molecular scales, fluctuations play a significant role and prevent biomolecular processes from always proceeding in a preferred direction, raising the question of how limited amounts of free energy can be dissipated to obtain directed progress. We examine the system and process characteristics that efficiently break time-reversal symmetry at fixed energy loss; in particular for a simple model of a molecular machine, an intermediate energy barrier produces unusually high asymmetry for a given dissipation. We relate the symmetry-breaking factors found in this model to recent observations of biomolecular machines.
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Affiliation(s)
- Aidan I Brown
- Department of Physics, Simon Fraser University, Burnaby, British Columbia, V5A1S6 Canada
| | - David A Sivak
- Department of Physics, Simon Fraser University, Burnaby, British Columbia, V5A1S6 Canada
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31
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Phillips RK, Peter LG, Gilbert SP, Rayment I. Family-specific Kinesin Structures Reveal Neck-linker Length Based on Initiation of the Coiled-coil. J Biol Chem 2016; 291:20372-86. [PMID: 27462072 DOI: 10.1074/jbc.m116.737577] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Indexed: 12/24/2022] Open
Abstract
Kinesin-1, -2, -5, and -7 generate processive hand-over-hand 8-nm steps to transport intracellular cargoes toward the microtubule plus end. This processive motility requires gating mechanisms to coordinate the mechanochemical cycles of the two motor heads to sustain the processive run. A key structural element believed to regulate the degree of processivity is the neck-linker, a short peptide of 12-18 residues, which connects the motor domain to its coiled-coil stalk. Although a shorter neck-linker has been correlated with longer run lengths, the structural data to support this hypothesis have been lacking. To test this hypothesis, seven kinesin structures were determined by x-ray crystallography. Each included the neck-linker motif, followed by helix α7 that constitutes the start of the coiled-coil stalk. In the majority of the structures, the neck-linker length differed from predictions because helix α7, which initiates the coiled-coil, started earlier in the sequence than predicted. A further examination of structures in the Protein Data Bank reveals that there is a great disparity between the predicted and observed starting residues. This suggests that an accurate prediction of the start of a coiled-coil is currently difficult to achieve. These results are significant because they now exclude simple comparisons between members of the kinesin superfamily and add a further layer of complexity when interpreting the results of mutagenesis or protein fusion. They also re-emphasize the need to consider factors beyond the kinesin neck-linker motif when attempting to understand how inter-head communication is tuned to achieve the degree of processivity required for cellular function.
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Affiliation(s)
- Rebecca K Phillips
- From the Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706 and
| | - Logan G Peter
- From the Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706 and
| | - Susan P Gilbert
- the Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Ivan Rayment
- From the Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706 and
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32
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Chen GY, Mickolajczyk KJ, Hancock WO. The Kinesin-5 Chemomechanical Cycle Is Dominated by a Two-heads-bound State. J Biol Chem 2016; 291:20283-20294. [PMID: 27402829 DOI: 10.1074/jbc.m116.730697] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Indexed: 12/29/2022] Open
Abstract
Single-molecule microscopy and stopped-flow kinetics assays were carried out to understand the microtubule polymerase activity of kinesin-5 (Eg5). Four lines of evidence argue that the motor primarily resides in a two-heads-bound (2HB) state. First, upon microtubule binding, dimeric Eg5 releases both bound ADPs. Second, microtubule dissociation in saturating ADP is 20-fold slower for the dimer than for the monomer. Third, ATP-triggered mant-ADP release is 5-fold faster than the stepping rate. Fourth, ATP binding is relatively fast when the motor is locked in a 2HB state. Shortening the neck-linker does not facilitate rear-head detachment, suggesting a minimal role for rear-head-gating. This 2HB state may enable Eg5 to stabilize incoming tubulin at the growing microtubule plus-end. The finding that slowly hydrolyzable ATP analogs trigger slower nucleotide release than ATP suggests that ATP hydrolysis in the bound head precedes stepping by the tethered head, leading to a mechanochemical cycle in which processivity is determined by the race between unbinding of the bound head and attachment of the tethered head.
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Affiliation(s)
- Geng-Yuan Chen
- From the Department of Biomedical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802
| | - Keith J Mickolajczyk
- From the Department of Biomedical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802
| | - William O Hancock
- From the Department of Biomedical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802
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