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Huang Huang - One of the best experts on this subject based on the ideXlab platform.

  • Regulation of the WD-Repeat/bHLH/MYB complex by gibberellin and jasmonate.
    Plant signaling & behavior, 2016
    Co-Authors: Haixia Tian, Susheng Song, Cuili Wang, Chunmei Ren, Huang Huang
    Abstract:

    The phytohormones gibberellin (GA) and jasmonate (JA) regulate various aspects of plant development, growth and defense. Previous studies showed that both DELLA repressors in GA pathway and JA-ZIM domain (JAZ) proteins in JA pathway interact with and repress the WD-Repeat/bHLH/MYB transcriptional complex to inhibit trichome initiation, and GA and JA respectively induce DELLAs and JAZs degradation to synergistically enhance trichome formation. In this study, we showed that the DELLA protein RGA and JAZ1 competitively bind to ENHANCER OF GLABRA3 (EGL3), a bHLH component of the WD-Repeat/bHLH/MYB complex. GA and JA differently affect the expression and protein stability of the components of the WD-Repeat/bHLH/MYB complex, and EGL3 and GL3 repress the expression of JAZ genes as a feedback. The novel findings help to understand the mechanism of the WD-Repeat/bHLH/MYB complex in GA/JA-regulated trichome formation.

  • Arabidopsis DELLA and JAZ Proteins Bind the WD-Repeat/ bHLH/MYB Complex to Modulate Gibberellin and Jasmonate Signaling Synergy
    The Plant cell, 2014
    Co-Authors: Huang Huang, Susheng Song, Jianbin Yan, Daoxin Xie
    Abstract:

    Integration of diverse environmental and endogenous signals to coordinately regulate growth, development, and defense is essential for plants to survive in their natural habitat. The hormonal signals gibberellin (GA) and jasmonate (JA) antagonistically and synergistically regulate diverse aspects of plant growth, development, and defense. GA and JA synergistically induce initiation of trichomes, which assist seed dispersal and act as barriers to protect plants against insect attack, pathogen infection, excessive water loss, and UV irradiation. However, the molecular mechanism underlying such synergism between GA and JA signaling remains unclear. In this study, we revealed a mechanism for GA and JA signaling synergy and identified a signaling complex of the GA pathway in regulation of trichome initiation. Molecular, biochemical, and genetic evidence showed that the WD-Repeat/bHLH/MYB complex acts as a direct target of DELLAs in the GA pathway and that both DELLAs and JAZs interacted with the WD-Repeat/bHLH/MYB complex to mediate synergism between GA and JA signaling in regulating trichome development. GA and JA induce degradation of DELLAs and JASMONATE ZIM-domain proteins to coordinately activate the WD-Repeat/bHLH/MYB complex and synergistically and mutually dependently induce trichome initiation. This study provides deep insights into the molecular mechanisms for integration of different hormonal signals to synergistically regulate plant development.

  • arabidopsis della and jaz proteins bind the WD Repeat bhlh myb complex to modulate gibberellin and jasmonate signaling synergy
    The Plant Cell, 2014
    Co-Authors: Huang Huang, Susheng Song, Jianbin Yan, Daoxin Xie
    Abstract:

    Integration of diverse environmental and endogenous signals to coordinately regulate growth, development, and defense is essential for plants to survive in their natural habitat. The hormonal signals gibberellin (GA) and jasmonate (JA) antagonistically and synergistically regulate diverse aspects of plant growth, development, and defense. GA and JA synergistically induce initiation of trichomes, which assist seed dispersal and act as barriers to protect plants against insect attack, pathogen infection, excessive water loss, and UV irradiation. However, the molecular mechanism underlying such synergism between GA and JA signaling remains unclear. In this study, we revealed a mechanism for GA and JA signaling synergy and identified a signaling complex of the GA pathway in regulation of trichome initiation. Molecular, biochemical, and genetic evidence showed that the WD-Repeat/bHLH/MYB complex acts as a direct target of DELLAs in the GA pathway and that both DELLAs and JAZs interacted with the WD-Repeat/bHLH/MYB complex to mediate synergism between GA and JA signaling in regulating trichome development. GA and JA induce degradation of DELLAs and JASMONATE ZIM-domain proteins to coordinately activate the WD-Repeat/bHLH/MYB complex and synergistically and mutually dependently induce trichome initiation. This study provides deep insights into the molecular mechanisms for integration of different hormonal signals to synergistically regulate plant development.

  • The Jasmonate-ZIM-Domain Proteins Interact with the WD-Repeat/bHLH/MYB Complexes to Regulate Jasmonate-Mediated Anthocyanin Accumulation and Trichome Initiation in Arabidopsis thaliana
    The Plant cell, 2011
    Co-Authors: Susheng Song, Wen Peng, Huang Huang, Yan Chen, Chunmei Ren, Qingcuo Ren, Meng Fan, Daoxin Xie
    Abstract:

    Jasmonates (JAs) mediate plant responses to insect attack, wounding, pathogen infection, stress, and UV damage and regulate plant fertility, anthocyanin accumulation, trichome formation, and many other plant developmental processes. Arabidopsis thaliana Jasmonate ZIM-domain (JAZ) proteins, substrates of the CORONATINE INSENSITIVE1 (COI1)–based SCF COI1 complex, negatively regulate these plant responses. Little is known about the molecular mechanism for JA regulation of anthocyanin accumulation and trichome initiation. In this study, we revealed that JAZ proteins interact with bHLH (Transparent Testa8, Glabra3 [GL3], and Enhancer of Glabra3 [EGL3]) and R2R3 MYB transcription factors (MYB75 and Glabra1), essential components of WD-Repeat/bHLH/MYB transcriptional complexes, to repress JA-regulated anthocyanin accumulation and trichome initiation. Genetic and physiological evidence showed that JA regulates WD-Repeat/bHLH/MYB complex-mediated anthocyanin accumulation and trichome initiation in a COI1 -dependent manner. Overexpression of the MYB transcription factor MYB75 and bHLH factors ( GL3 and EGL3 ) restored anthocyanin accumulation and trichome initiation in the coi1 mutant, respectively. We speculate that the JA-induced degradation of JAZ proteins abolishes the interactions of JAZ proteins with bHLH and MYB factors, allowing the transcriptional function of WD-Repeat/bHLH/MYB complexes, which subsequently activate respective downstream signal cascades to modulate anthocyanin accumulation and trichome initiation.

  • the jasmonate zim domain proteins interact with the WD Repeat bhlh myb complexes to regulate jasmonate mediated anthocyanin accumulation and trichome initiation in arabidopsis thaliana
    The Plant Cell, 2011
    Co-Authors: Tiancong Qi, Susheng Song, Dewei Wu, Huang Huang, Yan Chen, Wen Peng
    Abstract:

    Jasmonates (JAs) mediate plant responses to insect attack, wounding, pathogen infection, stress, and UV damage and regulate plant fertility, anthocyanin accumulation, trichome formation, and many other plant developmental processes. Arabidopsis thaliana Jasmonate ZIM-domain (JAZ) proteins, substrates of the CORONATINE INSENSITIVE1 (COI1)–based SCF COI1 complex, negatively regulate these plant responses. Little is known about the molecular mechanism for JA regulation of anthocyanin accumulation and trichome initiation. In this study, we revealed that JAZ proteins interact with bHLH (Transparent Testa8, Glabra3 [GL3], and Enhancer of Glabra3 [EGL3]) and R2R3 MYB transcription factors (MYB75 and Glabra1), essential components of WD-Repeat/bHLH/MYB transcriptional complexes, to repress JA-regulated anthocyanin accumulation and trichome initiation. Genetic and physiological evidence showed that JA regulates WD-Repeat/bHLH/MYB complex-mediated anthocyanin accumulation and trichome initiation in a COI1 -dependent manner. Overexpression of the MYB transcription factor MYB75 and bHLH factors ( GL3 and EGL3 ) restored anthocyanin accumulation and trichome initiation in the coi1 mutant, respectively. We speculate that the JA-induced degradation of JAZ proteins abolishes the interactions of JAZ proteins with bHLH and MYB factors, allowing the transcriptional function of WD-Repeat/bHLH/MYB complexes, which subsequently activate respective downstream signal cascades to modulate anthocyanin accumulation and trichome initiation.

Daoxin Xie - One of the best experts on this subject based on the ideXlab platform.

  • Arabidopsis DELLA and JAZ Proteins Bind the WD-Repeat/ bHLH/MYB Complex to Modulate Gibberellin and Jasmonate Signaling Synergy
    The Plant cell, 2014
    Co-Authors: Huang Huang, Susheng Song, Jianbin Yan, Daoxin Xie
    Abstract:

    Integration of diverse environmental and endogenous signals to coordinately regulate growth, development, and defense is essential for plants to survive in their natural habitat. The hormonal signals gibberellin (GA) and jasmonate (JA) antagonistically and synergistically regulate diverse aspects of plant growth, development, and defense. GA and JA synergistically induce initiation of trichomes, which assist seed dispersal and act as barriers to protect plants against insect attack, pathogen infection, excessive water loss, and UV irradiation. However, the molecular mechanism underlying such synergism between GA and JA signaling remains unclear. In this study, we revealed a mechanism for GA and JA signaling synergy and identified a signaling complex of the GA pathway in regulation of trichome initiation. Molecular, biochemical, and genetic evidence showed that the WD-Repeat/bHLH/MYB complex acts as a direct target of DELLAs in the GA pathway and that both DELLAs and JAZs interacted with the WD-Repeat/bHLH/MYB complex to mediate synergism between GA and JA signaling in regulating trichome development. GA and JA induce degradation of DELLAs and JASMONATE ZIM-domain proteins to coordinately activate the WD-Repeat/bHLH/MYB complex and synergistically and mutually dependently induce trichome initiation. This study provides deep insights into the molecular mechanisms for integration of different hormonal signals to synergistically regulate plant development.

  • arabidopsis della and jaz proteins bind the WD Repeat bhlh myb complex to modulate gibberellin and jasmonate signaling synergy
    The Plant Cell, 2014
    Co-Authors: Huang Huang, Susheng Song, Jianbin Yan, Daoxin Xie
    Abstract:

    Integration of diverse environmental and endogenous signals to coordinately regulate growth, development, and defense is essential for plants to survive in their natural habitat. The hormonal signals gibberellin (GA) and jasmonate (JA) antagonistically and synergistically regulate diverse aspects of plant growth, development, and defense. GA and JA synergistically induce initiation of trichomes, which assist seed dispersal and act as barriers to protect plants against insect attack, pathogen infection, excessive water loss, and UV irradiation. However, the molecular mechanism underlying such synergism between GA and JA signaling remains unclear. In this study, we revealed a mechanism for GA and JA signaling synergy and identified a signaling complex of the GA pathway in regulation of trichome initiation. Molecular, biochemical, and genetic evidence showed that the WD-Repeat/bHLH/MYB complex acts as a direct target of DELLAs in the GA pathway and that both DELLAs and JAZs interacted with the WD-Repeat/bHLH/MYB complex to mediate synergism between GA and JA signaling in regulating trichome development. GA and JA induce degradation of DELLAs and JASMONATE ZIM-domain proteins to coordinately activate the WD-Repeat/bHLH/MYB complex and synergistically and mutually dependently induce trichome initiation. This study provides deep insights into the molecular mechanisms for integration of different hormonal signals to synergistically regulate plant development.

  • The Jasmonate-ZIM-Domain Proteins Interact with the WD-Repeat/bHLH/MYB Complexes to Regulate Jasmonate-Mediated Anthocyanin Accumulation and Trichome Initiation in Arabidopsis thaliana
    The Plant cell, 2011
    Co-Authors: Susheng Song, Wen Peng, Huang Huang, Yan Chen, Chunmei Ren, Qingcuo Ren, Meng Fan, Daoxin Xie
    Abstract:

    Jasmonates (JAs) mediate plant responses to insect attack, wounding, pathogen infection, stress, and UV damage and regulate plant fertility, anthocyanin accumulation, trichome formation, and many other plant developmental processes. Arabidopsis thaliana Jasmonate ZIM-domain (JAZ) proteins, substrates of the CORONATINE INSENSITIVE1 (COI1)–based SCF COI1 complex, negatively regulate these plant responses. Little is known about the molecular mechanism for JA regulation of anthocyanin accumulation and trichome initiation. In this study, we revealed that JAZ proteins interact with bHLH (Transparent Testa8, Glabra3 [GL3], and Enhancer of Glabra3 [EGL3]) and R2R3 MYB transcription factors (MYB75 and Glabra1), essential components of WD-Repeat/bHLH/MYB transcriptional complexes, to repress JA-regulated anthocyanin accumulation and trichome initiation. Genetic and physiological evidence showed that JA regulates WD-Repeat/bHLH/MYB complex-mediated anthocyanin accumulation and trichome initiation in a COI1 -dependent manner. Overexpression of the MYB transcription factor MYB75 and bHLH factors ( GL3 and EGL3 ) restored anthocyanin accumulation and trichome initiation in the coi1 mutant, respectively. We speculate that the JA-induced degradation of JAZ proteins abolishes the interactions of JAZ proteins with bHLH and MYB factors, allowing the transcriptional function of WD-Repeat/bHLH/MYB complexes, which subsequently activate respective downstream signal cascades to modulate anthocyanin accumulation and trichome initiation.

Susheng Song - One of the best experts on this subject based on the ideXlab platform.

  • Regulation of the WD-Repeat/bHLH/MYB complex by gibberellin and jasmonate.
    Plant signaling & behavior, 2016
    Co-Authors: Haixia Tian, Susheng Song, Cuili Wang, Chunmei Ren, Huang Huang
    Abstract:

    The phytohormones gibberellin (GA) and jasmonate (JA) regulate various aspects of plant development, growth and defense. Previous studies showed that both DELLA repressors in GA pathway and JA-ZIM domain (JAZ) proteins in JA pathway interact with and repress the WD-Repeat/bHLH/MYB transcriptional complex to inhibit trichome initiation, and GA and JA respectively induce DELLAs and JAZs degradation to synergistically enhance trichome formation. In this study, we showed that the DELLA protein RGA and JAZ1 competitively bind to ENHANCER OF GLABRA3 (EGL3), a bHLH component of the WD-Repeat/bHLH/MYB complex. GA and JA differently affect the expression and protein stability of the components of the WD-Repeat/bHLH/MYB complex, and EGL3 and GL3 repress the expression of JAZ genes as a feedback. The novel findings help to understand the mechanism of the WD-Repeat/bHLH/MYB complex in GA/JA-regulated trichome formation.

  • Arabidopsis DELLA and JAZ Proteins Bind the WD-Repeat/ bHLH/MYB Complex to Modulate Gibberellin and Jasmonate Signaling Synergy
    The Plant cell, 2014
    Co-Authors: Huang Huang, Susheng Song, Jianbin Yan, Daoxin Xie
    Abstract:

    Integration of diverse environmental and endogenous signals to coordinately regulate growth, development, and defense is essential for plants to survive in their natural habitat. The hormonal signals gibberellin (GA) and jasmonate (JA) antagonistically and synergistically regulate diverse aspects of plant growth, development, and defense. GA and JA synergistically induce initiation of trichomes, which assist seed dispersal and act as barriers to protect plants against insect attack, pathogen infection, excessive water loss, and UV irradiation. However, the molecular mechanism underlying such synergism between GA and JA signaling remains unclear. In this study, we revealed a mechanism for GA and JA signaling synergy and identified a signaling complex of the GA pathway in regulation of trichome initiation. Molecular, biochemical, and genetic evidence showed that the WD-Repeat/bHLH/MYB complex acts as a direct target of DELLAs in the GA pathway and that both DELLAs and JAZs interacted with the WD-Repeat/bHLH/MYB complex to mediate synergism between GA and JA signaling in regulating trichome development. GA and JA induce degradation of DELLAs and JASMONATE ZIM-domain proteins to coordinately activate the WD-Repeat/bHLH/MYB complex and synergistically and mutually dependently induce trichome initiation. This study provides deep insights into the molecular mechanisms for integration of different hormonal signals to synergistically regulate plant development.

  • arabidopsis della and jaz proteins bind the WD Repeat bhlh myb complex to modulate gibberellin and jasmonate signaling synergy
    The Plant Cell, 2014
    Co-Authors: Huang Huang, Susheng Song, Jianbin Yan, Daoxin Xie
    Abstract:

    Integration of diverse environmental and endogenous signals to coordinately regulate growth, development, and defense is essential for plants to survive in their natural habitat. The hormonal signals gibberellin (GA) and jasmonate (JA) antagonistically and synergistically regulate diverse aspects of plant growth, development, and defense. GA and JA synergistically induce initiation of trichomes, which assist seed dispersal and act as barriers to protect plants against insect attack, pathogen infection, excessive water loss, and UV irradiation. However, the molecular mechanism underlying such synergism between GA and JA signaling remains unclear. In this study, we revealed a mechanism for GA and JA signaling synergy and identified a signaling complex of the GA pathway in regulation of trichome initiation. Molecular, biochemical, and genetic evidence showed that the WD-Repeat/bHLH/MYB complex acts as a direct target of DELLAs in the GA pathway and that both DELLAs and JAZs interacted with the WD-Repeat/bHLH/MYB complex to mediate synergism between GA and JA signaling in regulating trichome development. GA and JA induce degradation of DELLAs and JASMONATE ZIM-domain proteins to coordinately activate the WD-Repeat/bHLH/MYB complex and synergistically and mutually dependently induce trichome initiation. This study provides deep insights into the molecular mechanisms for integration of different hormonal signals to synergistically regulate plant development.

  • The Jasmonate-ZIM-Domain Proteins Interact with the WD-Repeat/bHLH/MYB Complexes to Regulate Jasmonate-Mediated Anthocyanin Accumulation and Trichome Initiation in Arabidopsis thaliana
    The Plant cell, 2011
    Co-Authors: Susheng Song, Wen Peng, Huang Huang, Yan Chen, Chunmei Ren, Qingcuo Ren, Meng Fan, Daoxin Xie
    Abstract:

    Jasmonates (JAs) mediate plant responses to insect attack, wounding, pathogen infection, stress, and UV damage and regulate plant fertility, anthocyanin accumulation, trichome formation, and many other plant developmental processes. Arabidopsis thaliana Jasmonate ZIM-domain (JAZ) proteins, substrates of the CORONATINE INSENSITIVE1 (COI1)–based SCF COI1 complex, negatively regulate these plant responses. Little is known about the molecular mechanism for JA regulation of anthocyanin accumulation and trichome initiation. In this study, we revealed that JAZ proteins interact with bHLH (Transparent Testa8, Glabra3 [GL3], and Enhancer of Glabra3 [EGL3]) and R2R3 MYB transcription factors (MYB75 and Glabra1), essential components of WD-Repeat/bHLH/MYB transcriptional complexes, to repress JA-regulated anthocyanin accumulation and trichome initiation. Genetic and physiological evidence showed that JA regulates WD-Repeat/bHLH/MYB complex-mediated anthocyanin accumulation and trichome initiation in a COI1 -dependent manner. Overexpression of the MYB transcription factor MYB75 and bHLH factors ( GL3 and EGL3 ) restored anthocyanin accumulation and trichome initiation in the coi1 mutant, respectively. We speculate that the JA-induced degradation of JAZ proteins abolishes the interactions of JAZ proteins with bHLH and MYB factors, allowing the transcriptional function of WD-Repeat/bHLH/MYB complexes, which subsequently activate respective downstream signal cascades to modulate anthocyanin accumulation and trichome initiation.

  • the jasmonate zim domain proteins interact with the WD Repeat bhlh myb complexes to regulate jasmonate mediated anthocyanin accumulation and trichome initiation in arabidopsis thaliana
    The Plant Cell, 2011
    Co-Authors: Tiancong Qi, Susheng Song, Dewei Wu, Huang Huang, Yan Chen, Wen Peng
    Abstract:

    Jasmonates (JAs) mediate plant responses to insect attack, wounding, pathogen infection, stress, and UV damage and regulate plant fertility, anthocyanin accumulation, trichome formation, and many other plant developmental processes. Arabidopsis thaliana Jasmonate ZIM-domain (JAZ) proteins, substrates of the CORONATINE INSENSITIVE1 (COI1)–based SCF COI1 complex, negatively regulate these plant responses. Little is known about the molecular mechanism for JA regulation of anthocyanin accumulation and trichome initiation. In this study, we revealed that JAZ proteins interact with bHLH (Transparent Testa8, Glabra3 [GL3], and Enhancer of Glabra3 [EGL3]) and R2R3 MYB transcription factors (MYB75 and Glabra1), essential components of WD-Repeat/bHLH/MYB transcriptional complexes, to repress JA-regulated anthocyanin accumulation and trichome initiation. Genetic and physiological evidence showed that JA regulates WD-Repeat/bHLH/MYB complex-mediated anthocyanin accumulation and trichome initiation in a COI1 -dependent manner. Overexpression of the MYB transcription factor MYB75 and bHLH factors ( GL3 and EGL3 ) restored anthocyanin accumulation and trichome initiation in the coi1 mutant, respectively. We speculate that the JA-induced degradation of JAZ proteins abolishes the interactions of JAZ proteins with bHLH and MYB factors, allowing the transcriptional function of WD-Repeat/bHLH/MYB complexes, which subsequently activate respective downstream signal cascades to modulate anthocyanin accumulation and trichome initiation.

Paul A. Steimle - One of the best experts on this subject based on the ideXlab platform.

  • WD Repeat Domain of Dictyostelium Myosin Heavy Chain Kinase C Functions in both Substrate Targeting and Cellular Localization
    Eukaryotic cell, 2009
    Co-Authors: Atiya Franklin, Linzi Hyatt, Alyssa Chowdhury, Paul A. Steimle
    Abstract:

    Myosin II disassembly in Dictyostelium discoideum is regulated by three structurally related myosin heavy chain kinases (myosin II heavy chain kinase A [MHCK-A], -B, and -C). We show that the WD Repeat domain of MHCK-C is unique in that it mediates both substrate targeting and subcellular localization, revealing a target for regulation that is distinct from those of the other MHCKs.

  • WD Repeat domains target dictyostelium myosin heavy chain kinases by binding directly to myosin filaments.
    The Journal of biological chemistry, 2000
    Co-Authors: Paul A. Steimle, Teresa V. Naismith, Lucila S. Licate, Thomas T. Egelhoff
    Abstract:

    Myosin heavy chain kinase (MHCK) A phosphorylates mapped sites at the C-terminal tail of Dictyostelium myosin II heavy chain, driving disassembly of myosin filaments both in vitro and in vivo. MHCK A is organized into three functional domains that include an N-terminal coiled-coil region, a central kinase catalytic domain unrelated to conventional protein kinases, and a WD Repeat domain at the C terminus. MHCK B is a homologue of MHCK A that possesses structurally related catalytic and WD Repeat domains. In the current study, we explored the role of the WD Repeat domains in defining the activities of both MHCK A and MHCK B using recombinant bacterially expressed truncations of these kinases either with or without their WD Repeat domains. We demonstrate that substrate targeting is a conserved function of the WD Repeat domains of both MHCK A and MHCK B and that this targeting is specific for Dictyostelium myosin II filaments. We also show that the mechanism of targeting involves direct binding of the WD Repeat domains to the myosin substrate. To our knowledge, this is the first report of WD Repeat domains physically targeting attached kinase domains to their substrates. The examples presented here may serve as a paradigm for enzyme targeting in other systems.

  • WD-Repeat domains target Dictyostelium myosin heavy chain kinase activities by binding directly to myosin II
    2000
    Co-Authors: Paul A. Steimle
    Abstract:

    Myosin heavy chain kinase (MHCK) A phosphorylates mapped sites at the C-terminal tail of Dictyostelium myosin II heavy chain, driving disassembly of myosin filaments both in vitro and in vivo. MHCK A is organized into three functional domains that include an N-terminal coiled-coil region, a central kinase catalytic domain unrelated to conventional protein kinases, and a WD Repeat domain at the C terminus. MHCK B is a homologue of MHCK A that possesses structurally related catalytic and WD Repeat domains. In the current study, we explored the role of the WD Repeat domains in defining the activities of both MHCK A and MHCK B using recombinant bacterially expressed truncations of these kinases either with or without their WD Repeat domains. We demonstrate that substrate targeting is a conserved function of the WD Repeat domains of both MHCK A and MHCK B and that this targeting is specific forDictyostelium myosin II filaments. We also show that the mechanism of targeting involves direct binding of the WD Repeat domains to the myosin substrate. To our knowledge, this is the first report of WD Repeat domains physically targeting attached kinase domains to their substrates. The examples presented here may serve as a paradigm for enzyme targeting in other systems.

Thomas T. Egelhoff - One of the best experts on this subject based on the ideXlab platform.

  • WD Repeat domains target dictyostelium myosin heavy chain kinases by binding directly to myosin filaments.
    The Journal of biological chemistry, 2000
    Co-Authors: Paul A. Steimle, Teresa V. Naismith, Lucila S. Licate, Thomas T. Egelhoff
    Abstract:

    Myosin heavy chain kinase (MHCK) A phosphorylates mapped sites at the C-terminal tail of Dictyostelium myosin II heavy chain, driving disassembly of myosin filaments both in vitro and in vivo. MHCK A is organized into three functional domains that include an N-terminal coiled-coil region, a central kinase catalytic domain unrelated to conventional protein kinases, and a WD Repeat domain at the C terminus. MHCK B is a homologue of MHCK A that possesses structurally related catalytic and WD Repeat domains. In the current study, we explored the role of the WD Repeat domains in defining the activities of both MHCK A and MHCK B using recombinant bacterially expressed truncations of these kinases either with or without their WD Repeat domains. We demonstrate that substrate targeting is a conserved function of the WD Repeat domains of both MHCK A and MHCK B and that this targeting is specific for Dictyostelium myosin II filaments. We also show that the mechanism of targeting involves direct binding of the WD Repeat domains to the myosin substrate. To our knowledge, this is the first report of WD Repeat domains physically targeting attached kinase domains to their substrates. The examples presented here may serve as a paradigm for enzyme targeting in other systems.

  • Dictyostelium Myosin Heavy Chain Kinase A Subdomains COILED-COIL AND WD Repeat ROLES IN OLIGOMERIZATION AND SUBSTRATE TARGETING
    The Journal of biological chemistry, 1997
    Co-Authors: Michael F. Kolman, Thomas T. Egelhoff
    Abstract:

    Abstract Myosin heavy chain kinase A (MHCK A) participates in the regulation of cytoskeletal myosin assembly inDictyostelium, driving filament disassembly via phosphorylation of sites in the myosin tail. MHCK A contains an amino-terminal coiled-coil domain, a novel central catalytic domain, and a carboxyl-terminal domain containing a 7-fold WD Repeat motif. We have overexpressed MHCK A truncation constructs to clarify the roles of each of these domains. Recombinant full-length MHCK A, MHCK A lacking the predicted coiled-coil domain, and MHCK A lacking the WD Repeat domain were expressed at high levels in Dictyostelium cells lacking endogenous MHCK A. Biochemical analysis of the purified proteins demonstrates that the putative coiled-coil domain is responsible for the oligomerization of the MHCK A holoenzyme. Removal of the WD Repeat domain had no effect on catalytic activity toward a synthetic peptide, but did result in a 95% loss of protein kinase activity when native myosin filaments were used as the substrate. Cellular analysis confirms that the same severe loss of activity against myosin occurs in vivo when the WD Repeat domain is eliminated. These results suggest that the WD Repeat domain of MHCK A serves to target this enzyme to its physiological substrate.