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Dudas EF, Tully MD, Foldes T, Kelly G, Tartaglia GG, Pastore A. The structural properties of full-length annexin A11. Front Mol Biosci 2024; 11:1347741. [PMID: 38516187 PMCID: PMC10955470 DOI: 10.3389/fmolb.2024.1347741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Accepted: 01/17/2024] [Indexed: 03/23/2024] Open
Abstract
Annexin A11 (ANXA11) is a calcium-dependent phospholipid-binding protein belonging to the annexin protein family and implicated in the neurodegenerative amyotrophic lateral sclerosis. Structurally, ANXA11 contains a conserved calcium-binding C-terminal domain common to all annexins and a putative intrinsically unfolded N-terminus specific for ANXA11. Little is known about the structure and functions of this region of the protein. By analogy with annexin A1, it was suggested that residues 38 to 59 within the ANXA11 N-terminus could form a helical region that would be involved in interactions. Interestingly, this region contains residues that, when mutated, may lead to clinical manifestations. In the present study, we have studied the structural features of the full-length protein with special attention to the N-terminal region using a combination of biophysical techniques which include nuclear magnetic resonance and small angle X-ray scattering. We show that the N-terminus is intrinsically disordered and that the overall features of the protein are not markedly affected by the presence of calcium. We also analyzed the 38-59 helix hypothesis using synthetic peptides spanning both the wild-type sequence and clinically relevant mutations. We show that the peptides have a remarkable character typical of a native helix and that mutations do not alter the behaviour suggesting that they are required for interactions rather than being structurally important. Our work paves the way to a more thorough understanding of the ANXA11 functions.
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Affiliation(s)
- Erika F. Dudas
- Dementia Research Institute at King’s College London, The Wohl Institute, London, United Kingdom
- European Synchrotron Radiation Facility, Grenoble, France
| | - Mark D. Tully
- European Synchrotron Radiation Facility, Grenoble, France
| | - Tamas Foldes
- University College London, Department of Physics and Astronomy, University College London, London, United Kingdom
- Institut de Biologie Structurale (IBS), Institut Laue-Langevin, University Grenoble Alpes, Grenoble, France
| | - Geoff Kelly
- MRC Biomedical NMR Centre, The Francis Crick Institute, London, United Kingdom
| | | | - Annalisa Pastore
- Dementia Research Institute at King’s College London, The Wohl Institute, London, United Kingdom
- European Synchrotron Radiation Facility, Grenoble, France
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2
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Korolkova OY, Widatalla SE, Williams SD, Whalen DS, Beasley HK, Ochieng J, Grewal T, Sakwe AM. Diverse Roles of Annexin A6 in Triple-Negative Breast Cancer Diagnosis, Prognosis and EGFR-Targeted Therapies. Cells 2020; 9:E1855. [PMID: 32784650 PMCID: PMC7465958 DOI: 10.3390/cells9081855] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 08/03/2020] [Accepted: 08/04/2020] [Indexed: 12/20/2022] Open
Abstract
The calcium (Ca2+)-dependent membrane-binding Annexin A6 (AnxA6), is a multifunctional, predominantly intracellular scaffolding protein, now known to play relevant roles in different cancer types through diverse, often cell-type-specific mechanisms. AnxA6 is differentially expressed in various stages/subtypes of several cancers, and its expression in certain tumor cells is also induced by a variety of pharmacological drugs. Together with the secretion of AnxA6 as a component of extracellular vesicles, this suggests that AnxA6 mediates distinct tumor progression patterns via extracellular and/or intracellular activities. Although it lacks enzymatic activity, some of the AnxA6-mediated functions involving membrane, nucleotide and cholesterol binding as well as the scaffolding of specific proteins or multifactorial protein complexes, suggest its potential utility in the diagnosis, prognosis and therapeutic strategies for various cancers. In breast cancer, the low AnxA6 expression levels in the more aggressive basal-like triple-negative breast cancer (TNBC) subtype correlate with its tumor suppressor activity and the poor overall survival of basal-like TNBC patients. In this review, we highlight the potential tumor suppressor function of AnxA6 in TNBC progression and metastasis, the relevance of AnxA6 in the diagnosis and prognosis of several cancers and discuss the concept of therapy-induced expression of AnxA6 as a novel mechanism for acquired resistance of TNBC to tyrosine kinase inhibitors.
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Affiliation(s)
- Olga Y. Korolkova
- Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA; (O.Y.K.); (S.E.W.); (S.D.W.); (D.S.W.); (H.K.B.); (J.O.)
| | - Sarrah E. Widatalla
- Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA; (O.Y.K.); (S.E.W.); (S.D.W.); (D.S.W.); (H.K.B.); (J.O.)
| | - Stephen D. Williams
- Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA; (O.Y.K.); (S.E.W.); (S.D.W.); (D.S.W.); (H.K.B.); (J.O.)
| | - Diva S. Whalen
- Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA; (O.Y.K.); (S.E.W.); (S.D.W.); (D.S.W.); (H.K.B.); (J.O.)
| | - Heather K. Beasley
- Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA; (O.Y.K.); (S.E.W.); (S.D.W.); (D.S.W.); (H.K.B.); (J.O.)
| | - Josiah Ochieng
- Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA; (O.Y.K.); (S.E.W.); (S.D.W.); (D.S.W.); (H.K.B.); (J.O.)
| | - Thomas Grewal
- School of Pharmacy, Faculty of Medicine and Health, University of Sydney, Sydney, NSW 2006, Australia;
| | - Amos M. Sakwe
- Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA; (O.Y.K.); (S.E.W.); (S.D.W.); (D.S.W.); (H.K.B.); (J.O.)
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3
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Localization of Annexin A6 in Matrix Vesicles During Physiological Mineralization. Int J Mol Sci 2020; 21:ijms21041367. [PMID: 32085611 PMCID: PMC7072960 DOI: 10.3390/ijms21041367] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2019] [Revised: 02/07/2020] [Accepted: 02/14/2020] [Indexed: 12/25/2022] Open
Abstract
Annexin A6 (AnxA6) is the largest member of the annexin family of proteins present in matrix vesicles (MVs). MVs are a special class of extracellular vesicles that serve as a nucleation site during cartilage, bone, and mantle dentin mineralization. In this study, we assessed the localization of AnxA6 in the MV membrane bilayer using native MVs and MV biomimetics. Biochemical analyses revealed that AnxA6 in MVs can be divided into three distinct groups. The first group corresponds to Ca2+-bound AnxA6 interacting with the inner leaflet of the MV membrane. The second group corresponds to AnxA6 localized on the surface of the outer leaflet. The third group corresponds to AnxA6 inserted in the membrane's hydrophobic bilayer and co-localized with cholesterol (Chol). Using monolayers and proteoliposomes composed of either dipalmitoylphosphatidylcholine (DPPC) to mimic the outer leaflet of the MV membrane bilayer or a 9:1 DPPC:dipalmitoylphosphatidylserine (DPPS) mixture to mimic the inner leaflet, with and without Ca2+, we confirmed that, in agreement with the biochemical data, AnxA6 interacted differently with the MV membrane. Thermodynamic analyses based on the measurement of surface pressure exclusion (πexc), enthalpy (ΔH), and phase transition cooperativity (Δt1/2) showed that AnxA6 interacted with DPPC and 9:1 DPPC:DPPS systems and that this interaction increased in the presence of Chol. The selective recruitment of AnxA6 by Chol was observed in MVs as probed by the addition of methyl-β-cyclodextrin (MβCD). AnxA6-lipid interaction was also Ca2+-dependent, as evidenced by the increase in πexc in negatively charged 9:1 DPPC:DPPS monolayers and the decrease in ΔH in 9:1 DPPC:DPPS proteoliposomes caused by the addition of AnxA6 in the presence of Ca2+ compared to DPPC zwitterionic bilayers. The interaction of AnxA6 with DPPC and 9:1 DPPC:DPPS systems was distinct even in the absence of Ca2+ as observed by the larger change in Δt1/2 in 9:1 DPPC:DPPS vesicles as compared to DPPC vesicles. Protrusions on the surface of DPPC proteoliposomes observed by atomic force microscopy suggested that oligomeric AnxA6 interacted with the vesicle membrane. Further work is needed to delineate possible functions of AnxA6 at its different localizations and ways of interaction with lipids.
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Groves P, Strzelecka-Kiliszek A, Sekrecka-Belniak A, Canales A, Jiménez-Barbero J, Bandorowicz-Pikula J, Pikula S, Cañada FJ. Exploring NMR methods as a tool to select suitable fluorescent nucleotide analogues. Org Biomol Chem 2014; 11:5332-8. [PMID: 23842795 DOI: 10.1039/c3ob40159f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Fluorescent analogues provide important tools for biochemical/biophysical research. However, the analogues contain chemical modifications much larger than those known to affect ligand-binding, such as the inversion of a carbon centre or substitution of an atom. We lack experimental tools and protocols to select the most appropriate fluorescent analogue. Herein, we use several NMR spectroscopy methods, including Saturation Transfer Difference (STD), STD competition and transferred nuclear Overhauser effect spectroscopy (Tr-NOESY), as tools to select appropriate fluorescent probes. Annexin A6 (AnxA6) is a ubiquitous protein that forms in vitro GTP-induced ion channels. We used this protein as a model and screened guanosine triphosphate (GTP) and four fluorescent analogues against AnxA6. STD reported that the GTP moiety of all ligands made similar contacts with the protein, despite additional interactions between the fluorescent tags and AnxA6. Competition STD experiments verified that the analogues and GTP bind to the same site. Tr-NOESY indicated that the bound conformation of the base relative to ribose is altered for some analogues compared to GTP. MANT-GTP or the BODIPY thioester of guanosine 5'-O-(3-thiotriphosphate) are the most suitable fluorescent analogues for AnxA6, according to NMR. These results reveal NMR as a useful technique to select and design proper fluorescent tags for biochemical/biophysical assays.
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Affiliation(s)
- Patrick Groves
- Chemical Biology Division, Instituto de Tecnologia Química e Biológica (ITQB-UNL), Oeiras, Portugal.
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5
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Clark GB, Morgan RO, Fernandez MP, Roux SJ. Evolutionary adaptation of plant annexins has diversified their molecular structures, interactions and functional roles. THE NEW PHYTOLOGIST 2012; 196:695-712. [PMID: 22994944 DOI: 10.1111/j.1469-8137.2012.04308.x] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Accepted: 07/29/2012] [Indexed: 05/04/2023]
Abstract
Annexins are an homologous, structurally related superfamily of proteins known to associate with membrane lipid and cytoskeletal components. Their involvement in membrane organization, vesicle trafficking and signaling is fundamental to cellular processes such as growth, differentiation, secretion and repair. Annexins exist in some prokaryotes and all eukaryotic phyla within which plant annexins represent a monophyletic clade of homologs descended from green algae. Genomic, proteomic and transcriptomic approaches have provided data on the diversity, cellular localization and expression patterns of different plant annexins. The availability of 35 complete plant genomes has enabled systematic comparative analysis to determine phylogenetic relationships, characterize structures and observe functional specificity between and within individual subfamilies. Short amino termini and selective erosion of the canonical type 2 calcium coordinating sites in domains 2 and 3 are typical of plant annexins. The convergent evolution of alternate functional motifs such as 'KGD', redox-sensitive Cys and hydrophobic Trp/Phe residues argues for their functional relevance and contribution to mechanistic diversity in plant annexins. This review examines recent findings and advances in plant annexin research with special focus on their structural diversity, cellular and molecular interactions and their potential integrated functions in the broader context of physiological responses.
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Affiliation(s)
- Greg B Clark
- Section of Molecular Cell and Developmental Biology, University of Texas, Austin, TX, 78713, USA
| | - Reginald O Morgan
- Department of Biochemistry and Molecular Biology, Faculty of Medicine and University Institute of Biotechnology of Asturias, University of Oviedo, E-33006, Oviedo, Spain
| | - Maria-Pilar Fernandez
- Department of Biochemistry and Molecular Biology, Faculty of Medicine and University Institute of Biotechnology of Asturias, University of Oviedo, E-33006, Oviedo, Spain
| | - Stanley J Roux
- Section of Molecular Cell and Developmental Biology, University of Texas, Austin, TX, 78713, USA
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6
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Podszywalow-Bartnicka P, Kosiorek M, Piwocka K, Sikora E, Zablocki K, Pikula S. Role of annexin A6 isoforms in catecholamine secretion by PC12 cells: distinct influence on calcium response. J Cell Biochem 2011; 111:168-78. [PMID: 20506562 DOI: 10.1002/jcb.22685] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Noradrenaline and adrenaline are secreted by adrenal medulla chromaffin cells via exocytosis. Exocytosis of catecholamines occurs after cell stimulation with various endogenous activators such as nicotine or after depolarization of the plasma membrane and is regulated by calcium ions. Cytosolic [Ca(2+)] increases in response to cell excitation and triggers a signal-initiated secretion. Annexins are known to participate in the regulation of membrane dynamics and are also considered to be involved in vesicular trafficking. Some experimental evidence suggests that annexins may participate in Ca(2+)-regulated catecholamine secretion. In this report the effect of annexin A6 (AnxA6) isoforms 1 and 2 on catecholamine secretion has been described. Overexpression of AnxA6 isoforms and AnxA6 knock-down in PC12 cells were accompanied by almost complete inhibition or a 20% enhancement of dopamine secretion, respectively. AnxA6-1 and AnxA6-2 overexpression reduced Delta[Ca(2+)](c) upon depolarization by 32% and 58%, respectively, while AnxA6 knock-down increased Delta[Ca(2+)](c) by 44%. The mechanism of AnxA6 action on Ca(2+) signalling is not well understood. Experimental evidence suggests that two AnxA6 isoforms interact with different targets engaged in regulation of calcium homeostasis in PC12 cells.
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Bandorowicz-Pikula J, Buchet R, Cañada FJ, Clémancey M, Groves P, Jiménez-Barbero J, Lancelin JM, Marcillat O, Pikula S, Sekrecka-Belniak A, Strzelecka-Kiliszek A. Characterization of caged compounds binding to proteins by NMR spectroscopy. Biochem Biophys Res Commun 2010; 400:447-51. [PMID: 20804737 DOI: 10.1016/j.bbrc.2010.08.104] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Accepted: 08/25/2010] [Indexed: 10/19/2022]
Abstract
Photolysable caged ligands are used to investigate protein function and activity. Here, we investigate the binding properties of caged nucleotides and their photo released products to well established but evolutionary and structurally unrelated nucleotide-binding proteins, rabbit muscle creatine kinase (RMCK) and human annexin A6 (hAnxA6), using saturation transfer difference NMR spectroscopy. We detect the binding of the caged nucleotides and discuss the general implications on interpreting data collected with photolysable caged ligands using different techniques. Strategies to avoid non-specific binding of caged compound to certain proteins are also suggested.
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Affiliation(s)
- Joanna Bandorowicz-Pikula
- Department of Biochemistry, Nencki Institute of Experimental Biology, 3 Pasteur Street, 02093 Warsaw, Poland
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8
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Sztolsztener ME, Strzelecka-Kiliszek A, Pikula S, Tylki-Szymanska A, Bandorowicz-Pikula J. Cholesterol as a factor regulating intracellular localization of annexin A6 in Niemann–Pick type C human skin fibroblasts. Arch Biochem Biophys 2010; 493:221-33. [DOI: 10.1016/j.abb.2009.11.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2009] [Revised: 10/27/2009] [Accepted: 11/02/2009] [Indexed: 11/25/2022]
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Mortimer JC, Laohavisit A, Macpherson N, Webb A, Brownlee C, Battey NH, Davies JM. Annexins: multifunctional components of growth and adaptation. JOURNAL OF EXPERIMENTAL BOTANY 2008; 59:533-44. [PMID: 18267940 DOI: 10.1093/jxb/erm344] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Plant annexins are ubiquitous, soluble proteins capable of Ca(2+)-dependent and Ca(2+)-independent binding to endomembranes and the plasma membrane. Some members of this multigene family are capable of binding to F-actin, hydrolysing ATP and GTP, acting as peroxidases or cation channels. These multifunctional proteins are distributed throughout the plant and throughout the life cycle. Their expression and intracellular localization are under developmental and environmental control. The in vitro properties of annexins and their known, dynamic distribution patterns suggest that they could be central regulators or effectors of plant growth and stress signalling. Potentially, they could operate in signalling pathways involving cytosolic free calcium and reactive oxygen species.
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Affiliation(s)
- Jennifer C Mortimer
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK
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10
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Groves P, Kövér KE, André S, Bandorowicz-Pikula J, Batta G, Bruix M, Buchet R, Canales A, Cañada FJ, Gabius HJ, Laurents DV, Naranjo JR, Palczewska M, Pikula S, Rial E, Strzelecka-Kiliszek A, Jiménez-Barbero J. Temperature dependence of ligand-protein complex formation as reflected by saturation transfer difference NMR experiments. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2007; 45:745-8. [PMID: 17638317 DOI: 10.1002/mrc.2041] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
We show that temperature is an important parameter for the sensitivity of saturation transfer difference (STD) spectroscopy. A decreased intensity of STD signals is observed for lactose binding to growth-regulatory galectin7 (p53-induced gene 1), as well as for nucleotide binding to annexin A6, when the temperature is increased from 281 to 298-310 K. Opposite temperature effects on STD intensity are observed for S-peptide binding to S-protein to reconstitute RNase S. However, the STD signals for tryptophan binding to downstream regulatory element antagonist modulator of the human prodynorphin gene (DREAM)are relatively unaffected between 281 and 298 K. The known kinetics of the binding of ATP by the uncoupling protein from brown adipose tissue mitochondria (UCP1) predicted an observable STD at 310 K, but rapid sample degradation limits the experiments to much lower temperatures. Temperature strongly influences the kinetics and affinity constant of various types of complex formation and in so doing influences the observed STD effects. Therefore, temperature can be exploited to facilitate the optimization of STD-based applications, and at the same time minimize the number of test samples. STD-based screening protocols to detect new target-specific compounds may yield a larger number of potential ligands if screened at various temperatures.
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Affiliation(s)
- Patrick Groves
- Department of Protein Science, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain.
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11
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Aukrust I, Hollås H, Strand E, Evensen L, Travé G, Flatmark T, Vedeler A. The mRNA-binding site of annexin A2 resides in helices C-D of its domain IV. J Mol Biol 2007; 368:1367-78. [PMID: 17395201 DOI: 10.1016/j.jmb.2007.02.094] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2007] [Revised: 02/26/2007] [Accepted: 02/27/2007] [Indexed: 11/27/2022]
Abstract
Annexin A2 (AnxA2) is a Ca(2+)-binding and phospholipid-binding protein involved in different intracellular processes including exocytosis, endocytosis and membrane-cytoskeleton movements. We have previously identified AnxA2 as an mRNA-binding protein present in cytoskeleton-bound polysomes, that binds to a specific approximately 100 nucleotide region in the 3'-untranslated region of c-myc and its cognate mRNA. In the present study, we show by UV cross-linking assays and surface plasmon resonance analyses that the mRNA-binding site of AnxA2 resides in its domain IV. Furthermore, the interaction of full-length AnxA2 with the 3'-untranslated region of anxA2 mRNA is Ca(2+)-dependent. By contrast, the interaction is Ca(2+)-independent for the isolated domain IV of AnxA2, suggesting that the mRNA-binding site is masked in Apo-AnxA2 and gains exposure through a Ca(2+)-induced conformational change of AnxA2 generating a favourable mRNA-binding site. The AnxA2-mRNA interaction is specific and involves helices C and D in domain IV of AnxA2, since point mutagenesis of several charged and polar exposed residues of these helices in the full-length protein strongly reduce RNA binding. The interaction appears to be sequential involving an initial phase of recognition dominated by electrostatic interactions, most likely between lysine residues and the phosphate backbone of RNA, followed by a second phase contributing to the specificity of the interaction.
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Affiliation(s)
- Ingvild Aukrust
- Department of Biomedicine, University of Bergen, Jonas Lies Vei 91, N-5009 Bergen, Norway
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12
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Balcerzak M, Bandorowicz-Pikula J, Buchet R, Pikula S. A novel retinoid binding property of human annexin A6. FEBS Lett 2006; 580:3065-9. [PMID: 16674946 DOI: 10.1016/j.febslet.2006.04.052] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2006] [Revised: 04/18/2006] [Accepted: 04/19/2006] [Indexed: 10/24/2022]
Abstract
Vitamin A (all-trans retinol) and all-trans retinoid acid (ATRA) interacted with human annexin A6 (AnxA6) as evidenced by AnxA6-induced blue shift of retinoid absorption maxima, by AnxA6-Trp fluorescence quenching and by a fluorescence resonance energy transfer from a Trp residue of AnxA6 to retinol. In addition, both retinoids stimulated the calcium-dependent binding of AnxA6 to liposomes, accompanied by oligomerization of AnxA6. Up to our knowledge, it is a first report supporting the hypothesis of a direct implication of AnxA6 in vitamin A-dependent tissue mineralization.
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Affiliation(s)
- Marcin Balcerzak
- Department of Cellular Biochemistry, Nencki Institute of Experimental Biology, 3 Pasteur Street, 02-093 Warsaw, Poland
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Golczak M, Kirilenko A, Bandorowicz-Pikula J, Desbat B, Pikula S. Structure of human annexin a6 at the air-water interface and in a membrane-bound state. Biophys J 2005; 87:1215-26. [PMID: 15298924 PMCID: PMC1304460 DOI: 10.1529/biophysj.103.038240] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
We postulate the existence of a pH-sensitive domain in annexin A6 (AnxA6), on the basis of our observation of pH-dependent conformational and orientation changes of this protein and its N- (AnxA6a) and C-terminal (AnxA6b) halves in the presence of lipids. Brewster angle microscopy shows that AnxA6, AnxA6a, and AnxA6b in the absence of lipids accumulate at the air-water interface and form a stable, homogeneous layer at pH below 6.0. Under these conditions polarization modulation IR absorption spectroscopy reveals significant conformational changes of AnxA6a whereas AnxA6b preserves its alpha-helical structure. The orientation of protein alpha-helices is parallel with respect to the interface. In the presence of lipids, polarization modulation IR reflection absorption spectroscopy experiments suggest that AnxA6a incorporates into the lipid/air interface, whereas AnxA6b is adsorbed under the lipid monolayer. In this case AnxA6a regains its alpha-helical structures. At a higher pressure of the lipid monolayer the average orientation of the alpha-helices of AnxA6a changes from flat to tilted by 45 degrees with respect to normal to the membrane interface. For AnxA6b no such changes are detected, even at a high pressure of the lipid monolayer-suggesting that the putative pH-sensitive domain of AnxA6 is localized in the N-terminal half of the protein.
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Affiliation(s)
- Marcin Golczak
- Department of Cellular Biochemistry, Nencki Institute of Experimental Biology, Warsaw, Poland
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Abstract
The tumor oncoproteins HRAS, KRAS, and NRAS are the founding members of a larger family of at least 35 related human proteins. Using a somewhat broader definition of sequence similarity reveals a more extended superfamily of more than 170 RAS-related proteins. The RAS superfamily of GTP (guanosine triphosphate) hydrolysis-coupled signal transduction relay proteins can be subclassified into RAS, RHO, RAB, and ARF families, as well as the closely related Galpha family. The members of each family can, in turn, be arranged into evolutionarily conserved branches. These groupings reflect structural, biochemical, and functional conservation. Recent findings have provided insights into the signaling characteristics of representative members of most RAS superfamily branches. The analysis presented here may serve as a guide for predicting the function of numerous uncharacterized superfamily members. Also described are guanosine triphosphatases (GTPases) distinct from members of the RAS superfamily. These related proteins employ GTP binding and GTPase domains in diverse structural contexts, expanding the scope of their function in humans.
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