1
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da Silva RM, Vital WO, Martins RS, Moraes J, Gomes H, Calixto C, Konnai S, Ohashi K, da Silva Vaz I, Logullo C. Differential expression of PEPCK isoforms is correlated to Aedes aegypti oogenesis and embryogenesis. Comp Biochem Physiol B Biochem Mol Biol 2021; 256:110618. [PMID: 34015437 DOI: 10.1016/j.cbpb.2021.110618] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 05/05/2021] [Accepted: 05/14/2021] [Indexed: 11/19/2022]
Abstract
The mosquito Aedes aegypti undertakes a shift in carbohydrate metabolism during embryogenesis, including an increase in the activity of phosphoenolpyruvate carboxykinase (PEPCK), a key gluconeogenic enzyme, at critical steps of embryo development. All eukaryotes studied to date present two PEPCK isoforms, namely PEPCK-M (mitochondrial) and PEPCK-C (cytosolic). In A. aegypti, however, these proteins are so far uncharacterized. In the present work we describe two A. aegypti PEPCK isoforms by sequence alignment, protein modeling, and transcription analysis in different tissues, as well as PEPCK enzymatic activity assays in mitochondrial and cytoplasmic compartments during oogenesis and embryogenesis. First, we characterized the protein sequences compared to other organisms, and identified conserved sites and key amino acids. We also performed structure modeling for AePEPCK(M) and AePEPCK(C), identifying highly conserved structural sites, as well as a signal peptide in AePEPCK(M) localized in a very hydrophobic region. Moreover, after blood meal and during mosquito oogenesis and embryogenesis, both PEPCKs isoforms showed different transcriptional profiles, suggesting that mRNA for the cytosolic form is transmitted maternally, whereas the mitochondrial form is synthesized by the zygote. Collectively, these results improve our understanding of mosquito physiology and may yield putative targets for developing new methods for A. aegypti control.
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Affiliation(s)
- Renato Martins da Silva
- Laboratório Integrado de Bioquímica Hatisaburo Masuda and Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Rio de Janeiro, RJ, Brazil
| | - Wagner Oliveira Vital
- Laboratório Integrado de Bioquímica Hatisaburo Masuda and Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | | | - Jorge Moraes
- Laboratório Integrado de Bioquímica Hatisaburo Masuda and Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | - Helga Gomes
- Laboratório Integrado de Bioquímica Hatisaburo Masuda and Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | - Christiano Calixto
- Laboratório Integrado de Bioquímica Hatisaburo Masuda and Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | - Satoru Konnai
- Laboratory of Infectious Diseases, Graduate School of Veterinary Medicine, Hokkaido University, Kita 18, Kita-ku Sapporo 060-0818, Japan
| | - Kazuhiko Ohashi
- Laboratory of Infectious Diseases, Graduate School of Veterinary Medicine, Hokkaido University, Kita 18, Kita-ku Sapporo 060-0818, Japan
| | - Itabajara da Silva Vaz
- Centro de Biotecnologia and Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil
| | - Carlos Logullo
- Laboratório Integrado de Bioquímica Hatisaburo Masuda and Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Rio de Janeiro, RJ, Brazil.
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2
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Sackmann E, Tanaka M. Critical role of lipid membranes in polarization and migration of cells: a biophysical view. Biophys Rev 2021; 13:123-138. [PMID: 33747247 PMCID: PMC7930189 DOI: 10.1007/s12551-021-00781-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Accepted: 01/03/2021] [Indexed: 12/15/2022] Open
Abstract
Cell migration plays vital roles in many biologically relevant processes such as tissue morphogenesis and cancer metastasis, and it has fascinated biophysicists over the past several decades. However, despite an increasing number of studies highlighting the orchestration of proteins involved in different signaling pathways, the functional roles of lipid membranes have been essentially overlooked. Lipid membranes are generally considered to be a functionless two-dimensional matrix of proteins, although many proteins regulating cell migration gain functions only after they are recruited to the membrane surface and self-organize their functional domains. In this review, we summarize how the logistical recruitment and release of proteins to and from lipid membranes coordinates complex spatiotemporal molecular processes. As predicted from the classical framework of the Smoluchowski equation of diffusion, lipid/protein membranes serve as a 2D reaction hub that contributes to the effective and robust regulation of polarization and migration of cells involving several competing pathways.
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Affiliation(s)
- Erich Sackmann
- Physics Department E22/E27, Technical University of Munich, James-Franck-Strasse, 85747 Garching, Germany
| | - Motomu Tanaka
- Physical Chemistry of Biosystems, Institute of Physical Chemistry, Heidelberg University, 69120 Heidelberg, Germany.,Center for Integrative Medicine and Physics, Institute for Advanced Study, Kyoto University, Kyoto, 606-8501 Japan
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3
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He W, Zhang J, Sachsenhauser V, Wang L, Bardwell JCA, Quan S. Increased surface charge in the protein chaperone Spy enhances its anti-aggregation activity. J Biol Chem 2020; 295:14488-14500. [PMID: 32817055 PMCID: PMC7573262 DOI: 10.1074/jbc.ra119.012300] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 07/31/2020] [Indexed: 12/21/2022] Open
Abstract
Chaperones are essential components of the protein homeostasis network. There is a growing interest in optimizing chaperone function, but exactly how to achieve this aim is unclear. Here, using a model chaperone, the bacterial protein Spy, we demonstrate that substitutions that alter the electrostatic potential of Spy's concave, client-binding surface enhance Spy's anti-aggregation activity. We show that this strategy is more efficient than one that enhances the hydrophobicity of Spy's surface. Our findings thus challenge the traditional notion that hydrophobic interactions are the major driving forces that guide chaperone-substrate binding. Kinetic data revealed that both charge- and hydrophobicity-enhanced Spy variants release clients more slowly, resulting in a greater "holdase" activity. However, increasing short-range hydrophobic interactions deleteriously affected Spy's ability to capture substrates, thus reducing its in vitro chaperone activity toward fast-aggregating substrates. Our strategy in chaperone surface engineering therefore sought to fine-tune the different molecular forces involved in chaperone-substrate interactions rather than focusing on enhancing hydrophobic interactions. These results improve our understanding of the mechanistic basis of chaperone-client interactions and illustrate how protein surface-based mutational strategies can facilitate the rational improvement of molecular chaperones.
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Affiliation(s)
- Wei He
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai Collaborative Innovation Center for Biomanufacturing, Shanghai, China
| | - Jiayin Zhang
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai Collaborative Innovation Center for Biomanufacturing, Shanghai, China
| | - Veronika Sachsenhauser
- Howard Hughes Medical Institute, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Lili Wang
- Howard Hughes Medical Institute, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - James C A Bardwell
- Howard Hughes Medical Institute, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Shu Quan
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai Collaborative Innovation Center for Biomanufacturing, Shanghai, China
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4
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Agarwal V, Naskar P, Agasti S, Khurana GK, Vishwakarma P, Lynn AM, Roche PA, Puri N. The cysteine-rich domain of synaptosomal-associated protein of 23 kDa (SNAP-23) regulates its membrane association and regulated exocytosis from mast cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2019; 1866:1618-1633. [PMID: 31260699 DOI: 10.1016/j.bbamcr.2019.06.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 06/25/2019] [Accepted: 06/26/2019] [Indexed: 01/04/2023]
Abstract
Synaptosomal-associated protein of 23 kDa (SNAP-23) plays an important role during regulated exocytosis of various inflammatory mediators, stored in secretory granules, from mast cells in response to physiological triggers. It is however synthesized as a soluble protein, and the mechanisms by which free SNAP-23 gets peripherally associated with membrane for the regulation of exocytosis, are poorly defined. SNAP-23 contains a hydrophobic domain with five closely spaced cysteines which get palmitoylated, and we show that SNAP-23 cysteine mutants show differential membrane association when transfected in rat basophilic leukemia (RBL) mast cells. SNAP-23 Cys- mutant, devoid of all five cysteines, and SNAP-23 P119A (proline to alanine) mutant, that likely interferes with palmitoylation of SNAP-23 by palmitoyl transferases are completely cytosolic. Mutating specific cysteines (Cys; C) to leucine or phenylalanine (L or F; retains hydrophobicity but lacks palmitoylation) partially decreases the membrane association of SNAP-23 which is further hampered by alanine (A; has lesser hydrophobicity, and lacks palmitoylation) mutation at C79, C80 or C83 position. Cloning a transmembrane domain MDR31-145 from multidrug resistance protein into SNAP-23 Cys- mutant is able to partially restore its membrane association. Regulated exocytosis studies using co-transfected human growth hormone (hGH) secretion reporter plasmid revealed that overexpression of SNAP-23 Cys- and P119A mutants significantly inhibits the overall extent of exocytosis from RBL mast cells, whereas expression of SNAP-23 Cys--MDR31-145 fusion protein is able to restore exocytosis. These results establish that the cysteine-rich domain of SNAP-23 regulates its membrane association and thereby also regulates exocytosis from mast cells.
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Affiliation(s)
- Vasudha Agarwal
- Cellular and Molecular Immunology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Pieu Naskar
- Cellular and Molecular Immunology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Suchhanda Agasti
- Cellular and Molecular Immunology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Gagandeep K Khurana
- Cellular and Molecular Immunology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Poonam Vishwakarma
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Andrew M Lynn
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Paul A Roche
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, United States of America
| | - Niti Puri
- Cellular and Molecular Immunology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
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5
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Baffi TR, Van AAN, Zhao W, Mills GB, Newton AC. Protein Kinase C Quality Control by Phosphatase PHLPP1 Unveils Loss-of-Function Mechanism in Cancer. Mol Cell 2019; 74:378-392.e5. [PMID: 30904392 DOI: 10.1016/j.molcel.2019.02.018] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Revised: 12/26/2018] [Accepted: 02/12/2019] [Indexed: 02/02/2023]
Abstract
Protein kinase C (PKC) isozymes function as tumor suppressors in increasing contexts. In contrast to oncogenic kinases, whose function is acutely regulated by transient phosphorylation, PKC is constitutively phosphorylated following biosynthesis to yield a stable, autoinhibited enzyme that is reversibly activated by second messengers. Here, we report that the phosphatase PHLPP1 opposes PKC phosphorylation during maturation, leading to the degradation of aberrantly active species that do not become autoinhibited. Cancer-associated hotspot mutations in the pseudosubstrate of PKCβ that impair autoinhibition result in dephosphorylated and unstable enzymes. Protein-level analysis reveals that PKCα is fully phosphorylated at the PHLPP site in over 5,000 patient tumors, with higher PKC levels correlating (1) inversely with PHLPP1 levels and (2) positively with improved survival in pancreatic adenocarcinoma. Thus, PHLPP1 provides a proofreading step that maintains the fidelity of PKC autoinhibition and reveals a prominent loss-of-function mechanism in cancer by suppressing the steady-state levels of PKC.
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Affiliation(s)
- Timothy R Baffi
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA; Biomedical Sciences Graduate Program, University of California at San Diego, La Jolla, CA 92093, USA
| | - An-Angela N Van
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA; Biomedical Sciences Graduate Program, University of California at San Diego, La Jolla, CA 92093, USA
| | - Wei Zhao
- Department of Systems Biology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Gordon B Mills
- Department of Systems Biology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Alexandra C Newton
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA.
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6
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Sackmann E. Viscoelasticity of single cells-from subcellular to cellular level. Semin Cell Dev Biol 2018; 93:2-15. [PMID: 30267805 DOI: 10.1016/j.semcdb.2018.09.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Revised: 08/27/2018] [Accepted: 09/21/2018] [Indexed: 12/12/2022]
Abstract
This review deals with insights into complex cellular structures and processes obtained by measuring viscoelastic impedances of the cell envelope and the cytoplasm by colloidal bead microrheometry. I first introduce a mechanical cell model that allows us to understand their unique ability of mechanical self-stabilization by actin microtubule crosstalk. In the second part, I show how cell movements can be driven by pulsatile or propagating solitary actin gelatin waves (SAGW) that are generated on nascent adhesion domains by logistically controlled membrane recruitment of functional proteins by electrostatic-hydrophobic forces. The global polarization of cell migration is guided by actin-microtubule crosstalk that is mediated by the Ca++ and strain-sensitive supramolecular scaffolding protein IQGAP. In the third part, I introduce the traction force microscopy as a tool to measure the forces between somatic cells and the tissue ´Here I show, how absolute values of viscoelastic impedances of the composite cell envelope can be obtained by deformation field mapping techniques. In the fourth part, it is shown how the dynamic mechanical properties of the active viscoplastic cytoplasmic space can be evaluated using colloidal beads as phantom endosomes. Separate measurements of velocity distributions of directed and random motions of phantom endosomes, yield local values of transport forces, viscosities and life times of directed motion along microtubules. The last part deals with biomimetic experiments allowing us to quantitatively evaluate the mechanical properties of passive and active actin networks on the basis of the percolation theory of gelation.
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Affiliation(s)
- Erich Sackmann
- Physics Department E22, Technical University Munich, James Franck Str. 1, D85747, Garching, Germany.
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7
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Singh RK, Kumar S, Tomar MS, Verma PK, Singh SP, Gautam PK, Acharya A. Classical Protein Kinase C: a novel kinase target in breast cancer. Clin Transl Oncol 2018; 21:259-267. [DOI: 10.1007/s12094-018-1929-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Accepted: 07/21/2018] [Indexed: 11/28/2022]
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8
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Galassi VV, Villarreal MA, Montich GG. Relevance of the protein macrodipole in the membrane-binding process. Interactions of fatty-acid binding proteins with cationic lipid membranes. PLoS One 2018. [PMID: 29518146 PMCID: PMC5843346 DOI: 10.1371/journal.pone.0194154] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The fatty acid-binding proteins L-BABP and Rep1-NCXSQ bind to anionic lipid membranes by electrostatic interactions. According to Molecular Dynamics (MD) simulations, the interaction of the protein macrodipole with the membrane electric field is a driving force for protein binding and orientation in the interface. To further explore this hypothesis, we studied the interactions of these proteins with cationic lipid membranes. As in the case of anionic lipid membranes, we found that both proteins, carrying a negative as well as a positive net charge, were bound to the positively charged membrane. Their major axis, those connecting the bottom of the β-barrel with the α-helix portal domain, were rotated about 180 degrees as compared with their orientations in the anionic lipid membranes. Fourier transform infrared (FTIR) spectroscopy of the proteins showed that the positively charged membranes were also able to induce conformational changes with a reduction of the β-strand proportion and an increase in α-helix secondary structure. Fatty acid-binding proteins (FABPs) are involved in several cell processes, such as maintaining lipid homeostasis in cells. They transport hydrophobic molecules in aqueous medium and deliver them into lipid membranes. Therefore, the interfacial orientation and conformation, both shown herein to be electrostatically determined, have a strong correlation with the specific mechanism by which each particular FABP exerts its biological function.
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Affiliation(s)
- Vanesa V. Galassi
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Biológica “Ranwel Caputto”, Córdoba, Argentina
- CONICET, Universidad Nacional de Córdoba, Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Córdoba, Argentina
| | - Marcos A. Villarreal
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Teórica y Computacional, Córdoba, Argentina
- CONICET, Universidad Nacional de Córdoba. Instituto de Investigaciones en Fisicoquímica de Córdoba (INFIQC), Córdoba, Argentina
| | - Guillermo G. Montich
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Biológica “Ranwel Caputto”, Córdoba, Argentina
- CONICET, Universidad Nacional de Córdoba, Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Córdoba, Argentina
- * E-mail:
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9
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Zhou HX, Pang X. Electrostatic Interactions in Protein Structure, Folding, Binding, and Condensation. Chem Rev 2018; 118:1691-1741. [PMID: 29319301 DOI: 10.1021/acs.chemrev.7b00305] [Citation(s) in RCA: 454] [Impact Index Per Article: 75.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Charged and polar groups, through forming ion pairs, hydrogen bonds, and other less specific electrostatic interactions, impart important properties to proteins. Modulation of the charges on the amino acids, e.g., by pH and by phosphorylation and dephosphorylation, have significant effects such as protein denaturation and switch-like response of signal transduction networks. This review aims to present a unifying theme among the various effects of protein charges and polar groups. Simple models will be used to illustrate basic ideas about electrostatic interactions in proteins, and these ideas in turn will be used to elucidate the roles of electrostatic interactions in protein structure, folding, binding, condensation, and related biological functions. In particular, we will examine how charged side chains are spatially distributed in various types of proteins and how electrostatic interactions affect thermodynamic and kinetic properties of proteins. Our hope is to capture both important historical developments and recent experimental and theoretical advances in quantifying electrostatic contributions of proteins.
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Affiliation(s)
- Huan-Xiang Zhou
- Department of Chemistry and Department of Physics, University of Illinois at Chicago , Chicago, Illinois 60607, United States.,Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
| | - Xiaodong Pang
- Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
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10
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Morales KA, Yang Y, Cole TR, Igumenova TI. Dynamic Response of the C2 Domain of Protein Kinase Cα to Ca 2+ Binding. Biophys J 2017; 111:1655-1667. [PMID: 27760353 DOI: 10.1016/j.bpj.2016.09.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 09/04/2016] [Accepted: 09/07/2016] [Indexed: 11/28/2022] Open
Abstract
Ca2+-dependent conserved-region 2 (C2) domains target their host signaling proteins to anionic membranes. The Ca2+-binding event is a prerequisite for membrane association. Here, we investigate multiscale metal-ion-dependent dynamics of the C2 domain of protein kinase Cα (C2α) using NMR spectroscopy. Interactions with metal ions attenuate microsecond-timescale motions of the loop regions, indicating that preorganization of the metal-binding loops occurs before membrane insertion. Binding of a full complement of Ca2+ ions has a profound effect on the millisecond-timescale dynamics of the N- and C-terminal regions of C2α. We propose that Ca2+ binding allosterically destabilizes the terminal regions of C2α and thereby facilitates the conformational rearrangement necessary for full membrane insertion and activation of protein kinase Cα.
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Affiliation(s)
- Krystal A Morales
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas
| | - Yuan Yang
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas
| | - Taylor R Cole
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas
| | - Tatyana I Igumenova
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas.
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11
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Katti S, Nyenhuis SB, Her B, Srivastava AK, Taylor AB, Hart PJ, Cafiso DS, Igumenova TI. Non-Native Metal Ion Reveals the Role of Electrostatics in Synaptotagmin 1-Membrane Interactions. Biochemistry 2017; 56:3283-3295. [PMID: 28574251 DOI: 10.1021/acs.biochem.7b00188] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
C2 domains are independently folded modules that often target their host proteins to anionic membranes in a Ca2+-dependent manner. In these cases, membrane association is triggered by Ca2+ binding to the negatively charged loop region of the C2 domain. Here, we used a non-native metal ion, Cd2+, in lieu of Ca2+ to gain insight into the contributions made by long-range Coulombic interactions and direct metal ion-lipid bridging to membrane binding. Using X-ray crystallography, NMR, Förster resonance energy transfer, and vesicle cosedimentation assays, we demonstrate that, although Cd2+ binds to the loop region of C2A/B domains of synaptotagmin 1 with high affinity, long-range Coulombic interactions are too weak to support membrane binding of individual domains. We attribute this behavior to two factors: the stoichiometry of Cd2+ binding to the loop regions of the C2A and C2B domains and the impaired ability of Cd2+ to directly coordinate the lipids. In contrast, electron paramagnetic resonance experiments revealed that Cd2+ does support membrane binding of the C2 domains in full-length synaptotagmin 1, where the high local lipid concentrations that result from membrane tethering can partially compensate for lack of a full complement of divalent metal ions and specific lipid coordination in Cd2+-complexed C2A/B domains. Our data suggest that long-range Coulombic interactions alone can drive the initial association of C2A/B with anionic membranes and that Ca2+ further augments membrane binding by the formation of metal ion-lipid coordination bonds and additional Ca2+ ion binding to the C2 domain loop regions.
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Affiliation(s)
- Sachin Katti
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Sarah B Nyenhuis
- Department of Chemistry and Biophysics Program, University of Virginia , Charlottesville, Virginia 22904, United States
| | - Bin Her
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Atul K Srivastava
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Alexander B Taylor
- Department of Biochemistry and Structural Biology and the X-ray Crystallography Core Laboratory, University of Texas Health Science Center at San Antonio , San Antonio, Texas 78229, United States
| | - P John Hart
- Department of Biochemistry and Structural Biology and the X-ray Crystallography Core Laboratory, University of Texas Health Science Center at San Antonio , San Antonio, Texas 78229, United States
| | - David S Cafiso
- Department of Chemistry and Biophysics Program, University of Virginia , Charlottesville, Virginia 22904, United States
| | - Tatyana I Igumenova
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
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12
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Bürstenbinder K, Möller B, Plötner R, Stamm G, Hause G, Mitra D, Abel S. The IQD Family of Calmodulin-Binding Proteins Links Calcium Signaling to Microtubules, Membrane Subdomains, and the Nucleus. PLANT PHYSIOLOGY 2017; 173:1692-1708. [PMID: 28115582 PMCID: PMC5338658 DOI: 10.1104/pp.16.01743] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 01/20/2017] [Indexed: 05/20/2023]
Abstract
Calcium (Ca2+) signaling and dynamic reorganization of the cytoskeleton are essential processes for the coordination and control of plant cell shape and cell growth. Calmodulin (CaM) and closely related calmodulin-like (CML) polypeptides are principal sensors of Ca2+ signals. CaM/CMLs decode and relay information encrypted by the second messenger via differential interactions with a wide spectrum of targets to modulate their diverse biochemical activities. The plant-specific IQ67 DOMAIN (IQD) family emerged as possibly the largest class of CaM-interacting proteins with undefined molecular functions and biological roles. Here, we show that the 33 members of the IQD family in Arabidopsis (Arabidopsis thaliana) differentially localize, using green fluorescent protein (GFP)-tagged proteins, to multiple and distinct subcellular sites, including microtubule (MT) arrays, plasma membrane subdomains, and nuclear compartments. Intriguingly, the various IQD-specific localization patterns coincide with the subcellular patterns of IQD-dependent recruitment of CaM, suggesting that the diverse IQD members sequester Ca2+-CaM signaling modules to specific subcellular sites for precise regulation of Ca2+-dependent processes. Because MT localization is a hallmark of most IQD family members, we quantitatively analyzed GFP-labeled MT arrays in Nicotiana benthamiana cells transiently expressing GFP-IQD fusions and observed IQD-specific MT patterns, which point to a role of IQDs in MT organization and dynamics. Indeed, stable overexpression of select IQD proteins in Arabidopsis altered cellular MT orientation, cell shape, and organ morphology. Because IQDs share biochemical properties with scaffold proteins, we propose that IQD families provide an assortment of platform proteins for integrating CaM-dependent Ca2+ signaling at multiple cellular sites to regulate cell function, shape, and growth.
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Affiliation(s)
- Katharina Bürstenbinder
- Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.);
- Institute of Computer Science (B.M.), Biocenter (G.H.), and Institute of Biochemistry and Biotechnology (S.A.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; and
- Department of Plant Sciences, University of California, Davis, California 95616 (S.A.)
| | - Birgit Möller
- Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.)
- Institute of Computer Science (B.M.), Biocenter (G.H.), and Institute of Biochemistry and Biotechnology (S.A.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; and
- Department of Plant Sciences, University of California, Davis, California 95616 (S.A.)
| | - Romina Plötner
- Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.)
- Institute of Computer Science (B.M.), Biocenter (G.H.), and Institute of Biochemistry and Biotechnology (S.A.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; and
- Department of Plant Sciences, University of California, Davis, California 95616 (S.A.)
| | - Gina Stamm
- Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.)
- Institute of Computer Science (B.M.), Biocenter (G.H.), and Institute of Biochemistry and Biotechnology (S.A.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; and
- Department of Plant Sciences, University of California, Davis, California 95616 (S.A.)
| | - Gerd Hause
- Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.)
- Institute of Computer Science (B.M.), Biocenter (G.H.), and Institute of Biochemistry and Biotechnology (S.A.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; and
- Department of Plant Sciences, University of California, Davis, California 95616 (S.A.)
| | - Dipannita Mitra
- Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.)
- Institute of Computer Science (B.M.), Biocenter (G.H.), and Institute of Biochemistry and Biotechnology (S.A.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; and
- Department of Plant Sciences, University of California, Davis, California 95616 (S.A.)
| | - Steffen Abel
- Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.)
- Institute of Computer Science (B.M.), Biocenter (G.H.), and Institute of Biochemistry and Biotechnology (S.A.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; and
- Department of Plant Sciences, University of California, Davis, California 95616 (S.A.)
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13
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Antal CE, Callender JA, Kornev AP, Taylor SS, Newton AC. Intramolecular C2 Domain-Mediated Autoinhibition of Protein Kinase C βII. Cell Rep 2015; 12:1252-60. [PMID: 26279568 DOI: 10.1016/j.celrep.2015.07.039] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Revised: 06/23/2015] [Accepted: 07/17/2015] [Indexed: 11/26/2022] Open
Abstract
The signaling output of protein kinase C (PKC) is exquisitely controlled, with its disruption resulting in pathophysiologies. Identifying the structural basis for autoinhibition is central to developing effective therapies for cancer, where PKC activity needs to be enhanced, or neurodegenerative diseases, where PKC activity should be inhibited. Here, we reinterpret a previously reported crystal structure of PKCβII and use docking and functional analysis to propose an alternative structure that is consistent with previous literature on PKC regulation. Mutagenesis of predicted contact residues establishes that the Ca(2+)-sensing C2 domain interacts intramolecularly with the kinase domain and the carboxyl-terminal tail, locking PKC in an inactive conformation. Ca(2+)-dependent bridging of the C2 domain to membranes provides the first step in activating PKC via conformational selection. Although the placement of the C1 domains remains to be determined, elucidation of the structural basis for autoinhibition of PKCβII unveils a unique direction for therapeutically targeting PKC.
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Affiliation(s)
- Corina E Antal
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92037, USA; Biomedical Sciences Graduate Program, University of California at San Diego, La Jolla, CA 92037, USA
| | - Julia A Callender
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92037, USA; Biomedical Sciences Graduate Program, University of California at San Diego, La Jolla, CA 92037, USA
| | - Alexandr P Kornev
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92037, USA
| | - Susan S Taylor
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92037, USA
| | - Alexandra C Newton
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92037, USA.
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14
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Abstract
Protein kinase C (PKC) is a family of Ser/Thr kinases that regulate a multitude of cellular processes through participation in the phosphoinositide signaling pathway. Significant research efforts have been directed at understanding the structure, function, and regulatory modes of the enzyme since its discovery and identification as the first receptor for tumor-promoting phorbol esters. The activation of PKC involves a transition from the cytosolic autoinhibited latent form to the membrane-associated active form. The membrane recruitment step is accompanied by the conformational rearrangement of the enzyme, which relieves autoinhibitory interactions and thereby allows PKC to phosphorylate its targets. The multidomain structure and intrinsic flexibility of PKC present remarkable challenges and opportunities for the biophysical and structural biology studies of this class of enzymes and their interactions with membranes, the major focus of this Current Topic. I will highlight the recent advances in the field, outline the current challenges, and identify areas where biophysics and structural biology approaches can provide insight into the isoenzyme-specific regulation of PKC activity.
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15
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Abstract
Precise control of the amplitude of protein kinase C (PKC) signalling is essential for cellular homoeostasis, and disruption of this control leads to pathophysiological states such as cancer, neurodegeneration and diabetes. For conventional and novel PKC, this amplitude is meticulously tuned by multiple inputs that regulate the amount of enzyme in the cell, its ability to sense its allosteric activator diacylglycerol, and protein scaffolds that co-ordinate access to substrates. Key to regulation of the signalling output of most PKC isoenzymes is the ability of cytosolic enzyme to respond to the membrane-embedded lipid second messenger, diacylglycerol, in a dynamic range that prevents signalling in the absence of agonists but allows efficient activation in response to small changes in diacylglycerol levels. The present review discusses the regulatory inputs that control the spatiotemporal dynamics of PKC signalling, with a focus on conventional and novel PKC isoenzymes.
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16
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Ambrozkiewicz MC, Kawabe H. HECT-type E3 ubiquitin ligases in nerve cell development and synapse physiology. FEBS Lett 2015; 589:1635-43. [PMID: 25979171 DOI: 10.1016/j.febslet.2015.05.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Revised: 05/03/2015] [Accepted: 05/05/2015] [Indexed: 12/21/2022]
Abstract
The development of neurons is precisely controlled. Nerve cells are born from progenitor cells, migrate to their future target sites, extend dendrites and an axon to form synapses, and thus establish neural networks. All these processes are governed by multiple intracellular signaling cascades, among which ubiquitylation has emerged as a potent regulatory principle that determines protein function and turnover. Dysfunctions of E3 ubiquitin ligases or aberrant ubiquitin signaling contribute to a variety of brain disorders like X-linked mental retardation, schizophrenia, autism or Parkinson's disease. In this review, we summarize recent findings about molecular pathways that involve E3 ligases of the Homologous to E6-AP C-terminus (HECT) family and that control neuritogenesis, neuronal polarity formation, and synaptic transmission.
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Affiliation(s)
- Mateusz Cyryl Ambrozkiewicz
- Max Planck Institute of Experimental Medicine, Department of Molecular Neurobiology, Hermann-Rein-Straße 3, D-37075 Göttingen, Germany.
| | - Hiroshi Kawabe
- Max Planck Institute of Experimental Medicine, Department of Molecular Neurobiology, Hermann-Rein-Straße 3, D-37075 Göttingen, Germany.
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17
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Hinks J, Poh WH, Chu JJH, Loo JSC, Bazan GC, Hancock LE, Wuertz S. Oligopolyphenylenevinylene-conjugated oligoelectrolyte membrane insertion molecules selectively disrupt cell envelopes of Gram-positive bacteria. Appl Environ Microbiol 2015; 81:1949-58. [PMID: 25576607 PMCID: PMC4345381 DOI: 10.1128/aem.03355-14] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 12/26/2014] [Indexed: 12/11/2022] Open
Abstract
The modification of microbial membranes to achieve biotechnological strain improvement with exogenous small molecules, such as oligopolyphenylenevinylene-conjugated oligoelectrolyte (OPV-COE) membrane insertion molecules (MIMs), is an emerging biotechnological field. Little is known about the interactions of OPV-COEs with their target, the bacterial envelope. We studied the toxicity of three previously reported OPV-COEs with a selection of Gram-negative and Gram-positive organisms and demonstrated that Gram-positive bacteria are more sensitive to OPV-COEs than Gram-negative bacteria. Transmission electron microscopy demonstrated that these MIMs disrupt microbial membranes and that this occurred to a much greater degree in Gram-positive organisms. We used a number of mutants to probe the nature of MIM interactions with the microbial envelope but were unable to align the membrane perturbation effects of these compounds to previously reported membrane disruption mechanisms of, for example, cationic antimicrobial peptides. Instead, the data support the notion that OPV-COEs disrupt microbial membranes through a suspected interaction with diphosphatidylglycerol (DPG), a major component of Gram-positive membranes. The integrity of model membranes containing elevated amounts of DPG was disrupted to a greater extent by MIMs than those prepared from Escherichia coli total lipid extracts alone.
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Affiliation(s)
- Jamie Hinks
- Singapore Centre on Environmental Life Sciences Engineering (SCELSE), Nanyang Technological University, Singapore, Singapore
| | - Wee Han Poh
- Singapore Centre on Environmental Life Sciences Engineering (SCELSE), Nanyang Technological University, Singapore, Singapore
| | - Justin Jang Hann Chu
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore, Singapore
| | - Joachim Say Chye Loo
- Singapore Centre on Environmental Life Sciences Engineering (SCELSE), Nanyang Technological University, Singapore, Singapore School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore
| | - Guillermo C Bazan
- Department of Chemistry & Biochemistry and Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, California, USA
| | - Lynn E Hancock
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA
| | - Stefan Wuertz
- Singapore Centre on Environmental Life Sciences Engineering (SCELSE), Nanyang Technological University, Singapore, Singapore School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Singapore Department of Civil and Environmental Engineering, University of California, Davis, California, USA
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18
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Li J, Ziemba BP, Falke J, Voth GA. Interactions of protein kinase C-α C1A and C1B domains with membranes: a combined computational and experimental study. J Am Chem Soc 2014; 136:11757-66. [PMID: 25075641 PMCID: PMC4140453 DOI: 10.1021/ja505369r] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Indexed: 02/01/2023]
Abstract
Protein kinase C-α (PKCα) has been studied widely as a paradigm for conventional PKCs, with two C1 domains (C1A and C1B) being important for the regulation and function of the kinase. However, it is challenging to explore these domains in membrane-bound environments with either simulations or experiments alone. In this work, we have combined modeling, simulations, and experiments to understand the molecular basis of the PKCα C1A and C1B domain interactions with membranes. Our atomistic simulations of the PKCα C1 domains reveal the dynamic interactions of the proteins with anionic lipids, as well as the conserved hydrogen bonds and the distinct nonpolar contacts formed with lipid activators. Corroborating evidence is obtained from additional simulations and experiments in terms of lipid binding and protein diffusion. Overall, our study, for the first time, explains with atomistic detail how the PKCα C1A and C1B domains interact differently with various lipids. On the molecular level, the information provided by our study helps to shed light on PKCα regulation and activation mechanism. The combined computational/experimental approach demonstrated in this work is anticipated to enable further studies to explore the roles of C1 domains in many signaling proteins and to better understand their molecular mechanisms in normal cellular function and disease development.
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Affiliation(s)
- Jianing Li
- Department
of Chemistry, Institute for Biophysical Dynamics, James Franck Institute
and Computation Institute, The University
of Chicago, 5735 South
Ellis Avenue, Chicago, Illinois 60637, United States
| | - Brian P. Ziemba
- Department
of Chemistry and Biochemistry and the Molecular Biophysics Program, University of Colorado at Boulder, Boulder, Colorado 80309, United States
| | - Joseph
J. Falke
- Department
of Chemistry and Biochemistry and the Molecular Biophysics Program, University of Colorado at Boulder, Boulder, Colorado 80309, United States
| | - Gregory A. Voth
- Department
of Chemistry, Institute for Biophysical Dynamics, James Franck Institute
and Computation Institute, The University
of Chicago, 5735 South
Ellis Avenue, Chicago, Illinois 60637, United States
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19
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Antal CE, Violin JD, Kunkel MT, Skovsø S, Newton AC. Intramolecular conformational changes optimize protein kinase C signaling. ACTA ACUST UNITED AC 2014; 21:459-469. [PMID: 24631122 DOI: 10.1016/j.chembiol.2014.02.008] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Revised: 01/31/2014] [Accepted: 02/02/2014] [Indexed: 11/25/2022]
Abstract
Optimal tuning of enzyme signaling is critical for cellular homeostasis. We use fluorescence resonance energy transfer reporters in live cells to follow conformational transitions that tune the affinity of a multidomain signal transducer, protein kinase C (PKC), for optimal response to second messengers. This enzyme comprises two diacylglycerol sensors, the C1A and C1B domains, that have a sufficiently high intrinsic affinity for ligand so that the enzyme would be in a ligand-engaged, active state if not for mechanisms that mask its domains. We show that both diacylglycerol sensors are exposed in newly synthesized PKC and that conformational transitions following priming phosphorylations mask the domains so that the lower affinity sensor, the C1B domain, is the primary diacylglycerol binder. The conformational rearrangements of PKC serve as a paradigm for how multimodule transducers optimize their dynamic range of signaling.
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Affiliation(s)
- Corina E Antal
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA; Biomedical Sciences Graduate Program, University of California at San Diego, La Jolla, CA 92093, USA
| | - Jonathan D Violin
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA; Biomedical Sciences Graduate Program, University of California at San Diego, La Jolla, CA 92093, USA
| | - Maya T Kunkel
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA
| | - Søs Skovsø
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA; Institute for Cellular and Molecular Medicine, Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen, Denmark
| | - Alexandra C Newton
- Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA.
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20
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The "memory kinases": roles of PKC isoforms in signal processing and memory formation. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 122:31-59. [PMID: 24484697 DOI: 10.1016/b978-0-12-420170-5.00002-7] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The protein kinase C (PKC) isoforms, which play an essential role in transmembrane signal conduction, can be viewed as a family of "memory kinases." Evidence is emerging that they are critically involved in memory acquisition and maintenance, in addition to their involvement in other functions of cells. Deficits in PKC signal cascades in neurons are one of the earliest abnormalities in the brains of patients suffering from Alzheimer's disease. Their dysfunction is also involved in several other types of memory impairments, including those related to emotion, mental retardation, brain injury, and vascular dementia/ischemic stroke. Inhibition of PKC activity leads to a reduced capacity of many types of learning and memory, but may have therapeutic values in treating substance abuse or aversive memories. PKC activators, on the other hand, have been shown to possess memory-enhancing and antidementia actions. PKC pharmacology may, therefore, represent an attractive area for developing effective cognitive drugs for the treatment of many types of memory disorders and dementias.
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21
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Classical protein kinases C are regulated by concerted interaction with lipids: the importance of phosphatidylinositol-4,5-bisphosphate. Biophys Rev 2013; 6:3-14. [PMID: 28509956 DOI: 10.1007/s12551-013-0125-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 10/03/2013] [Indexed: 10/26/2022] Open
Abstract
Classical protein kinase C (PKC) enzymes are known to be important factors in cell physiology both in terms of health and disease. They are activated by triggering signals that induce their translocation to membranes. The consensus view is that several secondary messengers are involved in this activation, such as cytosolic Ca2+ and diacylglycerol. Cytosolic Ca2+ bridges the C2 domain to anionic phospholipids as phosphatidylserine in the membrane, and diacylglycerol binds to the C1 domain. Both diacylglycerol and the increase in Ca2+ concentration are assumed to arise from the extracellular signal that triggers the hydrolysis of phosphatidylinositol-4,5-bisphosphate. However, results obtained during the last decade indicate that this phosphoinositide itself is also responsible for modulating classical PKC activity and its localization in the plasma membrane.
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