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Eriksen MS, Bramham CR. Molecular physiology of Arc/Arg3.1: The oligomeric state hypothesis of synaptic plasticity. Acta Physiol (Oxf) 2022; 236:e13886. [PMID: 36073248 PMCID: PMC9787330 DOI: 10.1111/apha.13886] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Revised: 08/15/2022] [Accepted: 09/05/2022] [Indexed: 01/29/2023]
Abstract
The immediate early gene, Arc, is a pivotal regulator of synaptic plasticity, memory, and cognitive flexibility. But what is Arc protein? How does it work? Inside the neuron, Arc is a protein interaction hub and dynamic regulator of intra-cellular signaling in synaptic plasticity. In remarkable contrast, Arc can also self-assemble into retrovirus-like capsids that are released in extracellular vesicles and capable of intercellular transfer of RNA. Elucidation of the molecular basis of Arc hub and capsid functions, and the relationship between them, is vital for progress. Here, we discuss recent findings on Arc structure-function and regulation of oligomerization that are giving insight into the molecular physiology of Arc. The unique features of mammalian Arc are emphasized, while drawing comparisons with Drosophila Arc and retroviral Gag. The Arc N-terminal domain, found only in mammals, is proposed to play a key role in regulating Arc hub signaling, oligomerization, and formation of capsids. Bringing together several lines of evidence, we hypothesize that Arc function in synaptic plasticity-long-term potentiation (LTP) and long-term depression (LTD)-are dictated by different oligomeric forms of Arc. Specifically, monomer/dimer function in LTP, tetramer function in basic LTD, and 32-unit oligomer function in enhanced LTD. The role of mammalian Arc capsids is unclear but likely depends on the cross-section of captured neuronal activity-induced RNAs. As the functional states of Arc are revealed, it may be possible to selectively manipulate specific forms of Arc-dependent plasticity and intercellular communication involved in brain function and dysfunction.
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Affiliation(s)
| | - Clive R. Bramham
- Department of BiomedicineUniversity of BergenBergenNorway,Mohn Research Center for the BrainUniversity of BergenBergenNorway
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2
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Development and Validation of Arc Nanobodies: New Tools for Probing Arc Dynamics and Function. Neurochem Res 2022; 47:2656-2666. [PMID: 35307777 PMCID: PMC9463278 DOI: 10.1007/s11064-022-03573-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 03/04/2022] [Accepted: 03/07/2022] [Indexed: 11/06/2022]
Abstract
Activity-regulated cytoskeleton-associated (Arc) protein plays key roles in long-term synaptic plasticity, memory, and cognitive flexibility. However, an integral understanding of Arc mechanisms is lacking. Arc is proposed to function as an interaction hub in neuronal dendrites and the nucleus, yet Arc can also form retrovirus-like capsids with proposed roles in intercellular communication. Here, we sought to develop anti-Arc nanobodies (ArcNbs) as new tools for probing Arc dynamics and function. Six ArcNbs representing different clonal lines were selected from immunized alpaca. Immunoblotting with recombinant ArcNbs fused to a small ALFA-epitope tag demonstrated binding to recombinant Arc as well as endogenous Arc from rat cortical tissue. ALFA-tagged ArcNb also provided efficient immunoprecipitation of stimulus-induced Arc after carbachol-treatment of SH-SY5Y neuroblastoma cells and induction of long-term potentiation in the rat dentate gyrus in vivo. Epitope mapping showed that all Nbs recognize the Arc C-terminal region containing the retroviral Gag capsid homology domain, comprised of tandem N- and C-lobes. ArcNbs E5 and H11 selectively bound the N-lobe, which harbors a peptide ligand binding pocket specific to mammals. Four additional ArcNbs bound the region containing the C-lobe and C-terminal tail. For use as genetically encoded fluorescent intrabodies, we show that ArcNbs fused to mScarlet-I are uniformly expressed, without aggregation, in the cytoplasm and nucleus of HEK293FT cells. Finally, mScarlet-I-ArcNb H11 expressed as intrabody selectively bound the N-lobe and enabled co-immunoprecipitation of full-length intracellular Arc. ArcNbs are versatile tools for live-cell labeling and purification of Arc, and interrogation of Arc capsid domain specific functions.
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Kang J, Smidtas L. Enthalpy-entropy compensation in the binding of peptide ligands to human Arc. Biochem Biophys Rep 2021; 27:101088. [PMID: 34368472 PMCID: PMC8326351 DOI: 10.1016/j.bbrep.2021.101088] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Revised: 07/20/2021] [Accepted: 07/21/2021] [Indexed: 01/02/2023] Open
Affiliation(s)
- Jonghoon Kang
- Department of Biology, Valdosta State University, Valdosta, GA, 31698, USA
| | - Lukas Smidtas
- Department of Biology, Valdosta State University, Valdosta, GA, 31698, USA
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Uusitalo M, Klenow MB, Laulumaa S, Blakeley MP, Simonsen AC, Ruskamo S, Kursula P. Human myelin protein P2: from crystallography to time-lapse membrane imaging and neuropathy-associated variants. FEBS J 2021; 288:6716-6735. [PMID: 34138518 DOI: 10.1111/febs.16079] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 06/10/2021] [Accepted: 06/16/2021] [Indexed: 12/11/2022]
Abstract
Peripheral myelin protein 2 (P2) is a fatty acid-binding protein expressed in vertebrate peripheral nervous system myelin, as well as in human astrocytes. Suggested functions of P2 include membrane stacking and lipid transport. Mutations in the PMP2 gene, encoding P2, are associated with Charcot-Marie-Tooth disease (CMT). Recent studies have revealed three novel PMP2 mutations in CMT patients. To shed light on the structure and function of these P2 variants, we used X-ray and neutron crystallography, small-angle X-ray scattering, circular dichroism spectroscopy, computer simulations and lipid binding assays. The crystal and solution structures of the I50del, M114T and V115A variants of P2 showed minor differences to the wild-type protein, whereas their thermal stability was reduced. Vesicle aggregation assays revealed no change in membrane stacking characteristics, while the variants showed altered fatty acid binding. Time-lapse imaging of lipid bilayers indicated formation of double-membrane structures induced by P2, which could be related to its function in stacking of two myelin membrane surfaces in vivo. In order to better understand the links between structure, dynamics and function, the crystal structure of perdeuterated P2 was refined from room temperature data using neutrons and X-rays, and the results were compared to simulations and cryocooled crystal structures. Our data indicate similar properties for all known human P2 CMT variants; while crystal structures are nearly identical, thermal stability and function of CMT variants are impaired. Our data provide new insights into the structure-function relationships and dynamics of P2 in health and disease.
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Affiliation(s)
- Maiju Uusitalo
- Faculty of Biochemistry and Molecular Medicine & Biocenter Oulu, University of Oulu, Finland
| | - Martin Berg Klenow
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, Denmark
| | - Saara Laulumaa
- Faculty of Biochemistry and Molecular Medicine & Biocenter Oulu, University of Oulu, Finland.,European Spallation Source, Lund, Sweden
| | | | - Adam Cohen Simonsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, Denmark
| | - Salla Ruskamo
- Faculty of Biochemistry and Molecular Medicine & Biocenter Oulu, University of Oulu, Finland
| | - Petri Kursula
- Faculty of Biochemistry and Molecular Medicine & Biocenter Oulu, University of Oulu, Finland.,Department of Biomedicine, University of Bergen, Norway
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Walczyk-Mooradally A, Holborn J, Singh K, Tyler M, Patnaik D, Wesseling H, Brandon NJ, Steen J, Graether SP, Haggarty SJ, Lalonde J. Phosphorylation-dependent control of Activity-regulated cytoskeleton-associated protein (Arc) protein by TNIK. J Neurochem 2021. [PMID: 34077555 DOI: 10.1111/jnc.15077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Activity-regulated cytoskeleton-associated protein (Arc) is an immediate early gene product that support neuroplastic changes important for cognitive function and memory formation. As a protein with homology to the retroviral Gag protein, a particular characteristic of Arc is its capacity to self-assemble into virus-like capsids that can package mRNAs and transfer those transcripts to other cells. Although a lot has been uncovered about the contributions of Arc to neuron biology and behavior, very little is known about how different functions of Arc are coordinately regulated both temporally and spatially in neurons. The answer to this question we hypothesized must involve the occurrence of different protein post-translational modifications acting to confer specificity. In this study, we used mass spectrometry and sequence prediction strategies to map novel Arc phosphorylation sites. Our approach led us to recognize serine 67 (S67) and threonine 278 (T278) as residues that can be modified by TNIK, which is a kinase abundantly expressed in neurons that shares many functional overlaps with Arc and has, along with its interacting proteins such as the NMDA receptor, and been implicated as a risk factor for psychiatric disorders. Furthermore, characterization of each residue using site-directed mutagenesis to create S67 and T278 mutant variants revealed that TNIK action at those amino acids can strongly influence Arc's subcellular distribution and self-assembly as capsids. Together, our findings reveal an unsuspected connection between Arc and TNIK. Better understanding of the interplay between these two proteins in neuronal cells could lead to new insights about apparition and progression of psychiatric disorders. Cover Image for this issue: https://doi.org/10.1111/jnc.15077.
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Affiliation(s)
| | - Jennifer Holborn
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Karamjeet Singh
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Marshall Tyler
- Massachusetts General Hospital, Centre for Genomic Medicine, Boston, MA, USA
| | - Debasis Patnaik
- Massachusetts General Hospital, Centre for Genomic Medicine, Boston, MA, USA
| | - Hendrik Wesseling
- Boston Children's Hospital, F.M. Kirby Center for Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Nicholas J Brandon
- Neuroscience, BioPharmaceuticals R&D, AstraZeneca Boston, Waltham, MA, USA
| | - Judith Steen
- Boston Children's Hospital, F.M. Kirby Center for Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Steffen P Graether
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Stephen J Haggarty
- Massachusetts General Hospital, Centre for Genomic Medicine, Boston, MA, USA
| | - Jasmin Lalonde
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
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Walczyk-Mooradally A, Holborn J, Singh K, Tyler M, Patnaik D, Wesseling H, Brandon NJ, Steen J, Graether SP, Haggarty SJ, Lalonde J. Phosphorylation-dependent control of Activity-regulated cytoskeleton-associated protein (Arc) protein by TNIK. J Neurochem 2021; 158:1058-1073. [PMID: 34077555 DOI: 10.1111/jnc.15440] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/24/2021] [Accepted: 05/24/2021] [Indexed: 12/21/2022]
Abstract
Activity-regulated cytoskeleton-associated protein (Arc) is an immediate early gene product that support neuroplastic changes important for cognitive function and memory formation. As a protein with homology to the retroviral Gag protein, a particular characteristic of Arc is its capacity to self-assemble into virus-like capsids that can package mRNAs and transfer those transcripts to other cells. Although a lot has been uncovered about the contributions of Arc to neuron biology and behavior, very little is known about how different functions of Arc are coordinately regulated both temporally and spatially in neurons. The answer to this question we hypothesized must involve the occurrence of different protein post-translational modifications acting to confer specificity. In this study, we used mass spectrometry and sequence prediction strategies to map novel Arc phosphorylation sites. Our approach led us to recognize serine 67 (S67) and threonine 278 (T278) as residues that can be modified by TNIK, which is a kinase abundantly expressed in neurons that shares many functional overlaps with Arc and has, along with its interacting proteins such as the NMDA receptor, and been implicated as a risk factor for psychiatric disorders. Furthermore, characterization of each residue using site-directed mutagenesis to create S67 and T278 mutant variants revealed that TNIK action at those amino acids can strongly influence Arc's subcellular distribution and self-assembly as capsids. Together, our findings reveal an unsuspected connection between Arc and TNIK. Better understanding of the interplay between these two proteins in neuronal cells could lead to new insights about apparition and progression of psychiatric disorders.
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Affiliation(s)
| | - Jennifer Holborn
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Karamjeet Singh
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Marshall Tyler
- Massachusetts General Hospital, Centre for Genomic Medicine, Boston, MA, USA
| | - Debasis Patnaik
- Massachusetts General Hospital, Centre for Genomic Medicine, Boston, MA, USA
| | - Hendrik Wesseling
- Boston Children's Hospital, F.M. Kirby Center for Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Nicholas J Brandon
- Neuroscience, BioPharmaceuticals R&D, AstraZeneca Boston, Waltham, MA, USA
| | - Judith Steen
- Boston Children's Hospital, F.M. Kirby Center for Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Steffen P Graether
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Stephen J Haggarty
- Massachusetts General Hospital, Centre for Genomic Medicine, Boston, MA, USA
| | - Jasmin Lalonde
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
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Crystal and solution structures reveal oligomerization of individual capsid homology domains of Drosophila Arc. PLoS One 2021; 16:e0251459. [PMID: 33989344 PMCID: PMC8121366 DOI: 10.1371/journal.pone.0251459] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 03/23/2021] [Indexed: 12/22/2022] Open
Abstract
Synaptic plasticity is vital for brain function and memory formation. One of the key proteins in long-term synaptic plasticity and memory is the activity-regulated cytoskeleton-associated protein (Arc). Mammalian Arc forms virus-like capsid structures in a process requiring the N-terminal domain and contains two C-terminal lobes that are structural homologues to retroviral capsids. Drosophila has two isoforms of Arc, dArc1 and dArc2, with low sequence similarity to mammalian Arc, but lacking a large N-terminal domain. Both dArc isoforms are related to the Ty3/gypsy retrotransposon capsid, consisting of N- and C-terminal lobes. Structures of dArc1, as well as capsids formed by both dArc isoforms, have been recently determined. We carried out structural characterization of the four individual dArc lobe domains. As opposed to the corresponding mammalian Arc lobe domains, which are monomeric, the dArc lobes were all oligomeric in solution, indicating a strong propensity for homophilic interactions. A truncated N-lobe from dArc2 formed a domain-swapped dimer in the crystal structure, resulting in a novel dimer interaction that could be relevant for capsid assembly or other dArc functions. This domain-swapped structure resembles the dimeric protein C of flavivirus capsids, as well as the structure of histones dimers, domain-swapped transcription factors, and membrane-interacting BAK domains. The strong oligomerization properties of the isolated dArc lobe domains explain the ability of dArc to form capsids in the absence of any large N-terminal domain, in contrast to the mammalian protein.
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