1
|
de Freitas Fernandes A, Leonardo DA, Cavini IA, Rosa HVD, Vargas JA, D'Muniz Pereira H, Nascimento AS, Garratt RC. Conservation and divergence of the G-interfaces of Drosophila melanogaster septins. Cytoskeleton (Hoboken) 2023; 80:153-168. [PMID: 36576069 DOI: 10.1002/cm.21740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2022] [Revised: 12/19/2022] [Accepted: 12/26/2022] [Indexed: 12/29/2022]
Abstract
Septins possess a conserved guanine nucleotide-binding (G) domain that participates in the stabilization of organized hetero-oligomeric complexes which assemble into filaments, rings and network-like structures. The fruit fly, Drosophila melanogaster, has five such septin genes encoding Sep1, Sep2, Sep4, Sep5 and Pnut. Here, we report the crystal structure of the heterodimer formed between the G-domains of Sep1 and Sep2, the first from an insect to be described to date. A G-interface stabilizes the dimer (in agreement with the expected arrangement for the Drosophila hexameric particle) and this bears significant resemblance to its human counterparts, even down to the level of individual amino acid interactions. On the other hand, a model for the G-interface formed between the two copies of Pnut which occupy the centre of the hexamer, shows important structural differences, including the loss of a highly favourable bifurcated salt-bridge network. Whereas wild-type Pnut purifies as a monomer, the reintroduction of the salt-bridge network results in stabilizing the dimeric interface in solution as shown by size exclusion chromatography and thermal stability measurements. Adaptive steered molecular dynamics reveals an unzipping mechanism for dimer dissociation which initiates at a point of electrostatic repulsion within the switch II region. Overall, the data contribute to a better understanding of the molecular interactions involved in septin assembly/disassembly.
Collapse
Affiliation(s)
| | | | | | | | - Jhon Antoni Vargas
- São Carlos Institute of Physics, University of São Paulo, São Carlos, Brazil
| | | | | | | |
Collapse
|
2
|
Padovani C, Jevtić P, Rapé M. Quality control of protein complex composition. Mol Cell 2022; 82:1439-1450. [PMID: 35316660 DOI: 10.1016/j.molcel.2022.02.029] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 01/26/2022] [Accepted: 02/21/2022] [Indexed: 12/13/2022]
Abstract
Eukaryotic cells possess hundreds of protein complexes that contain multiple subunits and must be formed at the correct time and place during development. Despite specific assembly pathways, cells frequently encounter complexes with missing or aberrant subunits that can disrupt important signaling events. Cells, therefore, employ several ubiquitin-dependent quality control pathways that can prevent, correct, or degrade flawed complexes. In this review, we will discuss our emerging understanding of such quality control of protein complex composition.
Collapse
Affiliation(s)
- Chris Padovani
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Predrag Jevtić
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Michael Rapé
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences (QB3), University of California at Berkeley, Berkeley, CA 94720, USA.
| |
Collapse
|
3
|
Iv F, Martins CS, Castro-Linares G, Taveneau C, Barbier P, Verdier-Pinard P, Camoin L, Audebert S, Tsai FC, Ramond L, Llewellyn A, Belhabib M, Nakazawa K, Di Cicco A, Vincentelli R, Wenger J, Cabantous S, Koenderink GH, Bertin A, Mavrakis M. Insights into animal septins using recombinant human septin octamers with distinct SEPT9 isoforms. J Cell Sci 2021; 134:jcs258484. [PMID: 34350965 DOI: 10.1242/jcs.258484] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 07/02/2021] [Indexed: 01/22/2023] Open
Abstract
Septin GTP-binding proteins contribute essential biological functions that range from the establishment of cell polarity to animal tissue morphogenesis. Human septins in cells form hetero-octameric septin complexes containing the ubiquitously expressed SEPT9 subunit (also known as SEPTIN9). Despite the established role of SEPT9 in mammalian development and human pathophysiology, biochemical and biophysical studies have relied on monomeric SEPT9, thus not recapitulating its native assembly into hetero-octameric complexes. We established a protocol that enabled, for the first time, the isolation of recombinant human septin octamers containing distinct SEPT9 isoforms. A combination of biochemical and biophysical assays confirmed the octameric nature of the isolated complexes in solution. Reconstitution studies showed that octamers with either a long or a short SEPT9 isoform form filament assemblies, and can directly bind and cross-link actin filaments, raising the possibility that septin-decorated actin structures in cells reflect direct actin-septin interactions. Recombinant SEPT9-containing octamers will make it possible to design cell-free assays to dissect the complex interactions of septins with cell membranes and the actin and microtubule cytoskeleton.
Collapse
Affiliation(s)
- Francois Iv
- Institut Fresnel, CNRS UMR7249, Aix Marseille Univ, Centrale Marseille, 13013 Marseille, France
| | - Carla Silva Martins
- Institut Fresnel, CNRS UMR7249, Aix Marseille Univ, Centrale Marseille, 13013 Marseille, France
| | - Gerard Castro-Linares
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, 2629 HZ Delft, The Netherlands
| | - Cyntia Taveneau
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR 168, Laboratoire Physico Chimie Curie, 75005 Paris, France
- ARC Centre of Excellence in Advanced Molecular Imaging, Monash University, Australia; Biomedicine Discovery Institute, Department of Biochemistry and Molecular Biology, Monash University, 3800 Clayton, Australia
| | - Pascale Barbier
- Aix-Marseille Univ, CNRS, UMR 7051, Institut de Neurophysiopathologie (INP), 13005 Marseille, France
| | - Pascal Verdier-Pinard
- Centre de Recherche en Cancérologie de Marseille (CRCM), INSERM, Institut Paoli-Calmettes, Aix Marseille Univ, CNRS, 13009 Marseille, France
| | - Luc Camoin
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille Protéomique, Marseille, France
| | - Stéphane Audebert
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille Protéomique, Marseille, France
| | - Feng-Ching Tsai
- Department of Living Matter, AMOLF, 1098 XG Amsterdam, The Netherlands
| | - Laurie Ramond
- Institut Fresnel, CNRS UMR7249, Aix Marseille Univ, Centrale Marseille, 13013 Marseille, France
| | - Alex Llewellyn
- Institut Fresnel, CNRS UMR7249, Aix Marseille Univ, Centrale Marseille, 13013 Marseille, France
| | - Mayssa Belhabib
- Institut Fresnel, CNRS UMR7249, Aix Marseille Univ, Centrale Marseille, 13013 Marseille, France
| | - Koyomi Nakazawa
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR 168, Laboratoire Physico Chimie Curie, 75005 Paris, France
| | - Aurélie Di Cicco
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR 168, Laboratoire Physico Chimie Curie, 75005 Paris, France
| | - Renaud Vincentelli
- Architecture et Fonction des Macromolécules Biologiques (AFMB), CNRS UMR7257, Aix Marseille Univ, 13009 Marseille, France
| | - Jerome Wenger
- Institut Fresnel, CNRS UMR7249, Aix Marseille Univ, Centrale Marseille, 13013 Marseille, France
| | - Stéphanie Cabantous
- Centre de Recherche en Cancérologie de Toulouse (CRCT), Inserm, Université Paul Sabatier-Toulouse III, CNRS, 31037 Toulouse, France
| | - Gijsje H Koenderink
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, 2629 HZ Delft, The Netherlands
- Department of Living Matter, AMOLF, 1098 XG Amsterdam, The Netherlands
| | - Aurélie Bertin
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR 168, Laboratoire Physico Chimie Curie, 75005 Paris, France
| | - Manos Mavrakis
- Institut Fresnel, CNRS UMR7249, Aix Marseille Univ, Centrale Marseille, 13013 Marseille, France
| |
Collapse
|
4
|
Chou HC, Bhalla K, Demerdesh OE, Klingbeil O, Hanington K, Aganezov S, Andrews P, Alsudani H, Chang K, Vakoc CR, Schatz MC, McCombie WR, Stillman B. The human origin recognition complex is essential for pre-RC assembly, mitosis, and maintenance of nuclear structure. eLife 2021; 10:61797. [PMID: 33522487 PMCID: PMC7877914 DOI: 10.7554/elife.61797] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 01/30/2021] [Indexed: 12/23/2022] Open
Abstract
The origin recognition complex (ORC) cooperates with CDC6, MCM2-7, and CDT1 to form pre-RC complexes at origins of DNA replication. Here, using tiling-sgRNA CRISPR screens, we report that each subunit of ORC and CDC6 is essential in human cells. Using an auxin-inducible degradation system, we created stable cell lines capable of ablating ORC2 rapidly, revealing multiple cell division cycle phenotypes. The primary defects in the absence of ORC2 were cells encountering difficulty in initiating DNA replication or progressing through the cell division cycle due to reduced MCM2-7 loading onto chromatin in G1 phase. The nuclei of ORC2-deficient cells were also large, with decompacted heterochromatin. Some ORC2-deficient cells that completed DNA replication entered into, but never exited mitosis. ORC1 knockout cells also demonstrated extremely slow cell proliferation and abnormal cell and nuclear morphology. Thus, ORC proteins and CDC6 are indispensable for normal cellular proliferation and contribute to nuclear organization.
Collapse
Affiliation(s)
- Hsiang-Chen Chou
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States.,Graduate Program in Molecular and Cellular Biology, Stony Brook University, Stony Brook, United States
| | - Kuhulika Bhalla
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Olaf Klingbeil
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Sergey Aganezov
- Department of Computer Science, Whiting School of Engineering, Johns Hopkins University, Baltimore, United States
| | - Peter Andrews
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | - Habeeb Alsudani
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | - Kenneth Chang
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Michael C Schatz
- Department of Computer Science, Whiting School of Engineering, Johns Hopkins University, Baltimore, United States
| | | | - Bruce Stillman
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| |
Collapse
|
5
|
Balasov M, Akhmetova K, Chesnokov I. Humanized Drosophila Model of the Meier-Gorlin Syndrome Reveals Conserved and Divergent Features of the Orc6 Protein. Genetics 2020; 216:995-1007. [PMID: 33037049 PMCID: PMC7768257 DOI: 10.1534/genetics.120.303698] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 10/06/2020] [Indexed: 11/18/2022] Open
Abstract
Meier-Gorlin syndrome (MGS) is a rare, autosomal recessive disorder characterized by microtia, primordial dwarfism, small ears, and skeletal abnormalities. Patients with MGS often carry mutations in genes encoding the subunits of the Origin Recognition Complex (ORC), components of the prereplicative complex and replication machinery. Orc6 is an important component of ORC and has functions in both DNA replication and cytokinesis. A mutation in the conserved C-terminal motif of Orc6 associated with MGS impedes the interaction of Orc6 with core ORC. Recently, a new mutation in Orc6 was also identified; however, it is localized in the N-terminal domain of the protein. To study the functions of Orc6, we used the human gene to rescue the orc6 deletion in Drosophila Using this "humanized" Orc6-based Drosophila model of MGS, we discovered that unlike the previous Y225S MGS mutation in Orc6, the K23E substitution in the N-terminal TFIIB-like domain of Orc6 disrupts the protein ability to bind DNA. Our studies revealed the importance of evolutionarily conserved and variable domains of Orc6 protein, and allowed the studies of human protein functions and the analysis of the critical amino acids in live animal heterologous system, as well as provided novel insights into the mechanisms underlying MGS pathology.
Collapse
Affiliation(s)
- Maxim Balasov
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Alabama at Birmingham, Alabama 35294
| | - Katarina Akhmetova
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Alabama at Birmingham, Alabama 35294
| | - Igor Chesnokov
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Alabama at Birmingham, Alabama 35294
| |
Collapse
|
6
|
Xu N, You Y, Liu C, Balasov M, Lun LT, Geng Y, Fung CP, Miao H, Tian H, Choy TT, Shi X, Fan Z, Zhou B, Akhmetova K, Din RU, Yang H, Hao Q, Qian P, Chesnokov I, Zhu G. Structural basis of DNA replication origin recognition by human Orc6 protein binding with DNA. Nucleic Acids Res 2020; 48:11146-11161. [PMID: 32986843 PMCID: PMC7641730 DOI: 10.1093/nar/gkaa751] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 08/18/2020] [Accepted: 09/19/2020] [Indexed: 01/08/2023] Open
Abstract
The six-subunit origin recognition complex (ORC), a DNA replication initiator, defines the localization of the origins of replication in eukaryotes. The Orc6 subunit is the smallest and the least conserved among ORC subunits. It is required for DNA replication and essential for viability in all species. Orc6 in metazoans carries a structural homology with transcription factor TFIIB and can bind DNA on its own. Here, we report a solution structure of the full-length human Orc6 (HsOrc6) alone and in a complex with DNA. We further showed that human Orc6 is composed of three independent domains: N-terminal, middle and C-terminal (HsOrc6-N, HsOrc6-M and HsOrc6-C). We also identified a distinct DNA-binding domain of human Orc6, named as HsOrc6-DBD. The detailed analysis of the structure revealed novel amino acid clusters important for the interaction with DNA. Alterations of these amino acids abolish DNA-binding ability of Orc6 and result in reduced levels of DNA replication. We propose that Orc6 is a DNA-binding subunit of human/metazoan ORC and may play roles in targeting, positioning and assembling the functional ORC at the origins.
Collapse
Affiliation(s)
- Naining Xu
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
- Department of Oral and Maxillofacial Surgery, Peking University ShenzhenHospital, Shenzhen Peking University-The Hong Kong University of Science and Technology Medical Center, Shenzhen, 518036, China
| | - Yingying You
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
- Department of Oncology, Xiangya Hospital, Central South University, 87 Xiangya Road, Changsha, 410008, Hunan, China
| | - Changdong Liu
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Maxim Balasov
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham School of Medicine, Birmingham, AL 35294, USA
| | - Lee Tung Lun
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Yanyan Geng
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Chun Po Fung
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Haitao Miao
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Honglei Tian
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - To To Choy
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Xiao Shi
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Zhuming Fan
- School of Biomedical Sciences, University of Hong Kong, 21 Sassoon Road, Hong Kong SAR, 00000, China
| | - Bo Zhou
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Katarina Akhmetova
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham School of Medicine, Birmingham, AL 35294, USA
| | - Rahman Ud Din
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Hongyu Yang
- Department of Oral and Maxillofacial Surgery, Peking University Shenzhen Hospital, Shenzhen Peking University, Shenzhen, 518036, China
| | - Quan Hao
- School of Biomedical Sciences, University of Hong Kong, 21 Sassoon Road, Hong Kong SAR, 00000, China
| | - Peiyuan Qian
- Department of Ocean Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Igor Chesnokov
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham School of Medicine, Birmingham, AL 35294, USA
| | - Guang Zhu
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
- State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| |
Collapse
|
7
|
SEPT7 regulates Ca 2+ entry through Orai channels in human neural progenitor cells and neurons. Cell Calcium 2020; 90:102252. [PMID: 32682163 DOI: 10.1016/j.ceca.2020.102252] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Revised: 06/25/2020] [Accepted: 07/06/2020] [Indexed: 12/16/2022]
Abstract
Human neural progenitor cells (hNPCs) are self-renewing cells of neural lineage that can be differentiated into neurons of different subtypes. Here we show that SEPT7, a member of the family of filament-forming GTPases called septins, prevents constitutive Ca2+ entry through the store-operated Ca2+ entry channel, Orai in hNPCs and in differentiated neurons and is thus required for neuronal calcium homeostasis. Previous work in Drosophila neurons has shown that loss of one copy of the evolutionarily-conserved dSEPT7 gene leads to elevated Ca2+ entry via Orai, in the absence of ER-Ca2+ store depletion. We have identified an N-terminal polybasic region of SEPT7, known to interact with membrane-localized phospholipids, as essential for spontaneous calcium entry through Orai in hNPCs, whereas the GTPase domain of dSEPT7 is dispensable for this purpose. Re-organisation of Orai1 and the ER-Ca2+ sensor STIM1 observed near the plasma membrane in SEPT7 KD hNPCs, supports the idea that Septin7 containing heteromers prevent Ca2+ entry through a fraction of STIM-Orai complexes. Possible mechanisms by which SEPT7 reduction leads to opening of Orai channels in the absence of store-depletion are discussed.
Collapse
|
8
|
Akhmetova KA, Chesnokov IN, Fedorova SA. [Functional Characterization of Septin Complexes]. Mol Biol (Mosk) 2018; 52:155-171. [PMID: 29695686 DOI: 10.7868/s0026898418020015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Accepted: 10/27/2016] [Indexed: 12/28/2022]
Abstract
Septins belong to a family of conserved GTP-binding proteins found in majority of eukaryotic species except for higher plants. Septins form nonpolar complexes that further polymerize into filaments and associate with cell membranes, thus comprising newly acknowledged cytoskeletal system. Septins participate in a variety of cell processes and contribute to various pathophysiological states, including tumorigenesis and neurodegeneration. Here, we review the structural and functional properties of septins and the regulation of their dynamics with special emphasis on the role of septin filaments as a cytoskeletal system and its interaction with actin and microtubule cytoskeletons. We also discuss how septins compartmentalize the cell by forming local protein-anchoring scaffolds and by providing barriers for the lateral diffusion of the membrane proteins.
Collapse
Affiliation(s)
- K A Akhmetova
- Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090 Russia.,University of Alabama at Birmingham, Birmingham, 35294 USA.,Novosibirsk National Research State University, Novosibirsk, 630090 Russia
| | - I N Chesnokov
- University of Alabama at Birmingham, Birmingham, 35294 USA
| | - S A Fedorova
- Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090 Russia.,Novosibirsk National Research State University, Novosibirsk, 630090 Russia.,
| |
Collapse
|
9
|
Abbey M, Gaestel M, Menon MB. Septins: Active GTPases or just GTP-binding proteins? Cytoskeleton (Hoboken) 2018; 76:55-62. [PMID: 29747238 DOI: 10.1002/cm.21451] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 04/24/2018] [Accepted: 05/05/2018] [Indexed: 01/19/2023]
Abstract
Septins are conserved cytoskeletal proteins with unique filament forming capabilities and roles in cytokinesis and cell morphogenesis. Septins undergo hetero-oligomerization and assemble into higher order structures including filaments, rings, and cages. Hetero- and homotypic interactions of septin isoforms involve alternating GTPase (G)-domain interfaces and those mediated by N- and C-terminal extensions. While most septins bind GTP, display weak GTP-hydrolysis activity and incorporate guanine nucleotides in their interaction interfaces, studies using GTPase-inactivating mutations have failed to conclusively establish a crucial role for GTPase activity in mediating septin functions. In this mini-review, we will critically assess the role of GTP-binding and -hydrolysis on septin assembly and function. The relevance of G-domain activity will also be discussed in the context of human septin mutations as well as the development of specific small-molecules targeting septin polymerization. As structural determinants of septin oligomer interfaces, G-domains are attractive targets for ligand-based inhibition of septin assembly. Whether such an intervention can predictably alter septin function is a major question for future research.
Collapse
Affiliation(s)
- Megha Abbey
- Hannover Medical School, Institute of Cell Biochemistry, Hannover, 30625, Germany
| | - Matthias Gaestel
- Hannover Medical School, Institute of Cell Biochemistry, Hannover, 30625, Germany
| | - Manoj B Menon
- Hannover Medical School, Institute of Cell Biochemistry, Hannover, 30625, Germany
| |
Collapse
|
10
|
Deb BK, Hasan G. SEPT7-mediated regulation of Ca 2+ entry through Orai channels requires other septin subunits. Cytoskeleton (Hoboken) 2018; 76:104-114. [PMID: 30004181 DOI: 10.1002/cm.21476] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2018] [Revised: 06/21/2018] [Accepted: 07/06/2018] [Indexed: 11/12/2022]
Abstract
Orai channels are plasma membrane resident Ca2+ channels that allow extracellular Ca2+ uptake after depletion of ER-Ca2+ stores by a process called store-operated Ca2+ entry (SOCE). Septins of the SEPT2 subgroup act as positive regulators of SOCE in human nonexcitable cells. SEPT2 subgroup septins form the central core of hetero-hexameric or hetero-octameric complexes with SEPT6, SEPT7 and SEPT9 subgroup septins. The presence of fewer septin encoding genes coupled with ease of genetic manipulation allows for better understanding of septin subgroup function in Drosophila. Our earlier findings show that although dSEPT7 reduction does not alter Orai-mediated Ca2+ entry during SOCE, it results in constitutive activation of Orai channels in resting neurons. Here, we have investigated the role of other septin subgroup members in regulating Orai channel activation in Drosophila neurons by both cellular and functional assays. We show that dSEPT1, a SEPT2 subgroup septin can exist in a complex with dSEPT2 and dSEPT7 in the central nervous system (CNS) of Drosophila. Our findings suggest that the nature of septin filaments and heteromers obtained after reducing septins of different subgroups alters their ability to regulate Orai channel opening. The molecular mechanisms underlying this complex regulation of Orai function by septins require further cellular investigations.
Collapse
Affiliation(s)
- Bipan K Deb
- National Centre for Biological Sciences (NCBS), Tata Institute of Fundamental Research, Bangalore, Karnataka, India
| | - Gaiti Hasan
- National Centre for Biological Sciences (NCBS), Tata Institute of Fundamental Research, Bangalore, Karnataka, India
| |
Collapse
|
11
|
|
12
|
Khan A, Newby J, Gladfelter AS. Control of septin filament flexibility and bundling by subunit composition and nucleotide interactions. Mol Biol Cell 2018; 29:702-712. [PMID: 29321251 PMCID: PMC6003234 DOI: 10.1091/mbc.e17-10-0608] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Revised: 12/22/2017] [Accepted: 01/04/2018] [Indexed: 01/18/2023] Open
Abstract
Septins self-assemble into heteromeric rods and filaments to act as scaffolds and modulate membrane properties. How cells tune the biophysical properties of septin filaments to control filament flexibility and length, and in turn the size, shape, and position of higher-order septin structures, is not well understood. We examined how rod composition and nucleotide availability influence physical properties of septins such as annealing, fragmentation, bundling, and bending. We found that septin complexes have symmetric termini, even when both Shs1 and Cdc11 are coexpressed. The relative proportion of Cdc11/Shs1 septin complexes controls the biophysical properties of filaments and influences the rate of annealing, fragmentation, and filament flexibility. Additionally, the presence and apparent exchange of guanine nucleotide also alters filament length and bundling. An Shs1 mutant that is predicted to alter nucleotide hydrolysis has altered filament length and dynamics in cells and impacts cell morphogenesis. These data show that modulating filament properties through rod composition and nucleotide binding can control formation of septin assemblies that have distinct physical properties and functions.
Collapse
Affiliation(s)
- Anum Khan
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
- Department of Biology, Dartmouth College, Hanover, NH 03755
| | - Jay Newby
- Department of Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Amy S Gladfelter
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| |
Collapse
|
13
|
Spiliotis ET. Spatial effects - site-specific regulation of actin and microtubule organization by septin GTPases. J Cell Sci 2018; 131:jcs207555. [PMID: 29326311 PMCID: PMC5818061 DOI: 10.1242/jcs.207555] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The actin and microtubule cytoskeletons comprise a variety of networks with distinct architectures, dynamics and protein composition. A fundamental question in eukaryotic cell biology is how these networks are spatially and temporally controlled, so they are positioned in the right intracellular places at the right time. While significant progress has been made in understanding the self-assembly of actin and microtubule networks, less is known about how they are patterned and regulated in a site-specific manner. In mammalian systems, septins are a large family of GTP-binding proteins that multimerize into higher-order structures, which associate with distinct subsets of actin filaments and microtubules, as well as membranes of specific curvature and lipid composition. Recent studies have shed more light on how septins interact with actin and microtubules, and raised the possibility that the cytoskeletal topology of septins is determined by their membrane specificity. Importantly, new functions have emerged for septins regarding the generation, maintenance and positioning of cytoskeletal networks with distinct organization and biochemical makeup. This Review presents new and past findings, and discusses septins as a unique regulatory module that instructs the local differentiation and positioning of distinct actin and microtubule networks.
Collapse
Affiliation(s)
- Elias T Spiliotis
- Drexel University, Department of Biology, Drexel University, Philadelphia, PA 19104, USA
| |
Collapse
|
14
|
Phosphorylation of Pnut in the Early Stages of Drosophila Embryo Development Affects Association of the Septin Complex with the Membrane and Is Important for Viability. G3-GENES GENOMES GENETICS 2018; 8:27-38. [PMID: 29079679 PMCID: PMC5765355 DOI: 10.1534/g3.117.300186] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Septin proteins are polymerizing GTPases that are found in most eukaryotic species. Septins are important for cytokinesis and participate in many processes involving spatial modifications of the cell cortex. In Drosophila, septin proteins Pnut, Sep1, and Sep2 form a hexameric septin complex. Here, we found that septin protein Pnut is phosphorylated during the first 2 hr of Drosophila embryo development. To study the effect of Pnut phosphorylation in a live organism, we created a new Drosophila pnut null mutant that allows for the analysis of Pnut mutations during embryogenesis. To understand the functional significance of Pnut phosphorylation, Drosophila strains carrying nonphosphorylatable and phospho-mimetic mutant pnut transgenes were established. The expression of the nonphosphorylatable Pnut protein resulted in semilethality and abnormal protein localization, whereas the expression of the phospho-mimetic mutant form of Pnut disrupted the assembly of a functional septin complex and septin filament formation in vitro. Overall, our findings indicate that the controlled phosphorylation of Pnut plays an important role in regulating septin complex functions during organism development.
Collapse
|
15
|
Popova VV, Brechalov AV, Georgieva SG, Kopytova DV. Nonreplicative functions of the origin recognition complex. Nucleus 2018; 9:460-473. [PMID: 30196754 PMCID: PMC6244734 DOI: 10.1080/19491034.2018.1516484] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 08/04/2018] [Accepted: 08/16/2018] [Indexed: 12/14/2022] Open
Abstract
Origin recognition complex (ORC), a heteromeric six-subunit complex, is the central component of the eukaryotic pre-replication complex. Recent data from yeast, frogs, flies and mammals present compelling evidence that ORC and its individual subunits have nonreplicative functions as well. The majority of these functions, such as heterochromatin formation, chromosome condensation, and segregation are dependent on ORC-DNA interactions. Furthermore, ORC is involved in the control of cell division via its participation in centrosome duplication and cytokinesis. Recent findings have also demonstrated a direct interaction between ORC and mRNPs and highlighted an essential role of ORC in mRNA nuclear export. Along with the growth of evolutionary complexity of organisms, ORC complex functions become more elaborate and new functions of the ORC sub-complexes and individual subunits have emerged.
Collapse
Affiliation(s)
- Varvara V. Popova
- Department of Transcription Regulation and Chromatin Dynamics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Alexander V. Brechalov
- Department of Transcription Regulation and Chromatin Dynamics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Sofia G. Georgieva
- Department of Transcription Regulation and Chromatin Dynamics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Daria V. Kopytova
- Department of Transcription Regulation and Chromatin Dynamics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| |
Collapse
|
16
|
Busby T, Meissner JM, Styers ML, Bhatt J, Kaushik A, Hjelmeland AB, Sztul E. The Arf activator GBF1 localizes to plasma membrane sites involved in cell adhesion and motility. CELLULAR LOGISTICS 2017; 7:e1308900. [PMID: 28702273 DOI: 10.1080/21592799.2017.1308900] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 02/20/2017] [Accepted: 03/14/2017] [Indexed: 10/24/2022]
Affiliation(s)
- Theodore Busby
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Justyna M Meissner
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Melanie L Styers
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jay Bhatt
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Akhil Kaushik
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Anita B Hjelmeland
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Elizabeth Sztul
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| |
Collapse
|
17
|
Akhmetova KA, Dorogova NV, Bolobolova EU, Chesnokov IN, Fedorova SA. The Role of Pnut and its Functional Domains in Drosophila Spermatogenesis. RUSSIAN JOURNAL OF GENETICS. APPLIED RESEARCH 2017; 7:29-35. [PMID: 34306739 PMCID: PMC8297777 DOI: 10.1134/s2079059717010026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The Drosophila Pnut protein belongs to the family of septins, which are conserved GTPases participating in cytokinesis and many more other fundamental cellular processes. Because of their filamentous appearance, membrane association, and functions, septins are considered as the fourth component of the cytoskeleton, along with actin, microtubules, and intermediate filaments. However, septins are much less studied than the other cytoskeleton elements. We had previously demonstrated that the deletion of the pnut gene leads to mitotic abnormalities in somatic cells. The goal of this work was to study the role of the pnut in Drosophila spermatogenesis. We designed a construct for pnut RNA interference allowing pnut expression to be suppressed ectopically. We analyzed the effect of pnut RNA interference on Drosophila spermatogenesis. Germline cells at the earliest stages of spermatogenesis were the most sensitive to Pnut depletion: the suppression of the pnut expression at these stages leads to male sterility as a result of immotile sperm. The testes of these sterile males did not show any significant meiotic defects; the axonemes and mitochondria were normal. We also analyzed the effect of mutations in the Pnut's conservative domains on Drosophila spermatogenesis. Mutations in the GTPase domain resulted in cyst elongation defects. Deletions of the C-terminal domain led to abnormal testis morphology. Both the GTPase domain and C-terminal domain mutant males were sterile and produced immotile sperm. To summarize, we showed that Pnut participates in spermiogenesis, that is, the late stages of spermatogenesis, when major morphological changes in spermatocytes occur.
Collapse
Affiliation(s)
- K. A. Akhmetova
- Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
- University of Alabama at Birmingham, Birmingham, United States
- Novosibirsk State University, Novosibirsk, Russia
| | - N. V. Dorogova
- Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
| | - E. U. Bolobolova
- Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
| | - I. N. Chesnokov
- University of Alabama at Birmingham, Birmingham, United States
| | - S. A. Fedorova
- Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
- Novosibirsk State University, Novosibirsk, Russia
| |
Collapse
|
18
|
Deb BK, Hasan G. Regulation of Store-Operated Ca 2+ Entry by Septins. Front Cell Dev Biol 2016; 4:142. [PMID: 28018901 PMCID: PMC5156677 DOI: 10.3389/fcell.2016.00142] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 12/02/2016] [Indexed: 01/10/2023] Open
Abstract
The mechanism of store-operated Ca2+ entry (SOCE) brings extracellular Ca2+ into cells after depletion of intracellular Ca2+ stores. Regulation of Ca2+ homeostasis by SOCE helps control various intracellular signaling functions in both non-excitable and excitable cells. Whereas essential components of the SOCE pathway are well characterized, molecular mechanisms underlying regulation of this pathway need investigation. A class of proteins recently demonstrated as regulating SOCE is septins. These are filament-forming GTPases that assemble into higher order structures. One of their most studied cellular functions is as a molecular scaffold that creates diffusion barriers in membranes for a variety of cellular processes. Septins regulate SOCE in mammalian non-excitable cells and in Drosophila neurons. However, the molecular mechanism of SOCE-regulation by septins and the contribution of different subgroups of septins to SOCE-regulation remain to be understood. The regulation of SOCE is relevant in multiple cellular contexts as well as in diseases, such as the Severe Combined Immunodeficiency (SCID) syndrome and neurodegenerative syndromes like Alzheimer's, Spino-Cerebellar Ataxias and Parkinson's. Moreover, Drosophila neurons, where loss of SOCE leads to flight deficits, are a possible cellular template for understanding the molecular basis of neuronal deficits associated with loss of either the Inositol-1,4,5-trisphosphate receptor (IP3R1), a key activator of neuronal SOCE or the Endoplasmic reticulum resident Ca2+ sensor STIM1 (Stromal Interaction Molecule) in mouse. This perspective summarizes our current understanding of septins as regulators of SOCE and discusses the implications for mammalian neuronal function.
Collapse
Affiliation(s)
- Bipan K Deb
- National Centre for Biological Sciences, Tata Institute of Fundamental Research Bangalore, India
| | - Gaiti Hasan
- National Centre for Biological Sciences, Tata Institute of Fundamental Research Bangalore, India
| |
Collapse
|
19
|
Abstract
Functional studies in Drosophila have been key for establishing a role for the septin family of proteins in animal cell division and thus extending for the first time observations from the budding yeast to animal cells. Visualizing the distribution of specific septins in different Drosophila tissues and, in particular, in the Drosophila embryo, together with biochemical and mutant phenotype data, has contributed important advances to our understanding of animal septin biology, suggesting roles in processes other than in cytokinesis. Septin localization using immunofluorescence assays has been possible due to the generation of antibodies against different Drosophila septins. The recent availability of lines expressing fluorescent protein fusions of specific septins further promises to facilitate studies on septin dynamics. Here, we provide protocols for preparing early Drosophila embryos to visualize septins using immunofluorescence assays and live fluorescence microscopy. The genetic tractability of the Drosophila embryo together with its amenability to high-resolution fluorescence microscopy promises to provide novel insights into animal septin structure and function.
Collapse
Affiliation(s)
- M Mavrakis
- Aix Marseille Université, CNRS, Centrale Marseille, Institut Fresnel UMR 7249, Marseille, France.
| |
Collapse
|
20
|
GTPase domain driven dimerization of SEPT7 is dispensable for the critical role of septins in fibroblast cytokinesis. Sci Rep 2016; 6:20007. [PMID: 26818767 PMCID: PMC4730212 DOI: 10.1038/srep20007] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Accepted: 12/22/2015] [Indexed: 12/22/2022] Open
Abstract
Septin 7 (SEPT7) has been described to be essential for successful completion of cytokinesis in mouse fibroblasts, and Sept7-deficiency in fibroblasts constitutively results in multinucleated cells which stop proliferation. Using Sept7flox/floxfibroblasts we generated a cellular system, where the cytokinetic defects of Cre-mediated deletion of the Sept7 gene can be rescued by ectopically expressed doxycycline-inducible wild type SEPT7. Using this system, we analyzed the ability of SEPT7-mutants with alterations in their GTPase domain-dependent dimerization to prevent multinucleation and rescue proliferation. Although biochemical analysis of the mutants demonstrates differences in homo- and/or hetero-polymerization, in GTP-binding and/or GTPase activities, all analyzed mutants were able to rescue the cytokinesis phenotype of Sept7flox/floxfibroblasts associated with Cre-mediated deletion of endogenous Sept7. These findings indicate that the ability of septins to assemble into well-defined SEPT7-dimerization dependent native filaments is dispensable for cytokinesis in fibroblasts and opens the way to search for other mechanisms of the involvement of SEPT7 in cytokinesis.
Collapse
|
21
|
Balasov M, Akhmetova K, Chesnokov I. Drosophila model of Meier-Gorlin syndrome based on the mutation in a conserved C-Terminal domain of Orc6. Am J Med Genet A 2015; 167A:2533-40. [PMID: 26139588 DOI: 10.1002/ajmg.a.37214] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 06/05/2015] [Indexed: 11/09/2022]
Abstract
Meier-Gorlin syndrome (MGS) is an autosomal recessive disorder characterized by microtia, primordial dwarfism, small ears, and skeletal abnormalities. Patients with MGS often carry mutations in the genes encoding the components of the pre-replicative complex such as Origin Recognition Complex (ORC) subunits Orc1, Orc4, Orc6, and helicase loaders Cdt1 and Cdc6. Orc6 is an important component of ORC and has functions in both DNA replication and cytokinesis. Mutation in conserved C-terminal motif of Orc6 associated with MGS impedes the interaction of Orc6 with core ORC. In order to study the effects of MGS mutation in an animal model system we introduced MGS mutation in Orc6 and established Drosophila model of MGS. Mutant flies die at third instar larval stage with abnormal chromosomes and DNA replication defects. The lethality can be rescued by elevated expression of mutant Orc6 protein. Rescued MGS flies are unable to fly and display multiple planar cell polarity defects. © 2015 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Maxim Balasov
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, School of Medicine, Birmingham, Alabama
| | - Katarina Akhmetova
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, School of Medicine, Birmingham, Alabama.,The Federal Research Center Institute of Cytology and Genetics, Prospekt Lavrentyeva 10, Novosibirsk, Russian Federation.,Novosibirsk State University, Novosibirsk, Russian Federation
| | - Igor Chesnokov
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, School of Medicine, Birmingham, Alabama
| |
Collapse
|
22
|
Menon MB, Gaestel M. Sep(t)arate or not – how some cells take septin-independent routes through cytokinesis. J Cell Sci 2015; 128:1877-86. [PMID: 25690008 DOI: 10.1242/jcs.164830] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Cytokinesis is the final step of cell division, and is a process that requires a precisely coordinated molecular machinery to fully separate the cytoplasm of the parent cell and to establish the intact outer cell barrier of the daughter cells. Among various cytoskeletal proteins involved, septins are known to be essential mediators of cytokinesis. In this Commentary, we present recent observations that specific cell divisions can proceed in the absence of the core mammalian septin SEPT7 and its Drosophila homolog Peanut (Pnut) and that thus challenge the view that septins have an essential role in cytokinesis. In the pnut mutant neuroepithelium, orthogonal cell divisions are successfully completed. Similarly, in the mouse, Sept7-null mutant early embryonic cells and, more importantly, planktonically growing adult hematopoietic cells undergo productive proliferation. Hence, as discussed here, mechanisms must exist that compensate for the lack of SEPT7 and the other core septins in a cell-type-specific manner. Despite there being crucial non-canonical immune-relevant functions of septins, septin depletion is well tolerated by the hematopoietic system. Thus differential targeting of cytokinesis could form the basis for more specific anti-proliferative therapies to combat malignancies arising from cell types that require septins for cytokinesis, such as carcinomas and sarcomas, without impairing hematopoiesis that is less dependent on septin.
Collapse
Affiliation(s)
- Manoj B Menon
- Institute of Physiological Chemistry, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
| | - Matthias Gaestel
- Institute of Physiological Chemistry, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
| |
Collapse
|