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Cannon KS, Vargas-Muniz JM, Billington N, Seim I, Ekena J, Sellers JR, Gladfelter AS. A gene duplication of a septin reveals a developmentally regulated filament length control mechanism. J Cell Biol 2023; 222:e202204063. [PMID: 36786832 PMCID: PMC9960279 DOI: 10.1083/jcb.202204063] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 11/20/2022] [Accepted: 01/19/2023] [Indexed: 02/15/2023] Open
Abstract
Septins are a family of conserved filament-forming proteins that function in multiple cellular processes. The number of septin genes within an organism varies, and higher eukaryotes express many septin isoforms due to alternative splicing. It is unclear if different combinations of septin proteins in complex alter the polymers' biophysical properties. We report that a duplication event within the CDC11 locus in Ashbya gossypii gave rise to two similar but distinct Cdc11 proteins: Cdc11a and Cdc1b. CDC11b transcription is developmentally regulated, producing different amounts of Cdc11a- and Cdc11b-complexes in the lifecycle of Ashbya gossypii. Deletion of either gene results in distinct cell polarity defects, suggesting non-overlapping functions. Cdc11a and Cdc11b complexes have differences in filament length and membrane-binding ability. Thus, septin subunit composition has functional consequences on filament properties and cell morphogenesis. Small sequence differences elicit distinct biophysical properties and cell functions of septins, illuminating how gene duplication could be a driving force for septin gene expansions seen throughout the tree of life.
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Affiliation(s)
- Kevin S. Cannon
- Biology Department, University of North Carolina, Chapel Hill, NC, USA
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC, USA
| | - Jose M. Vargas-Muniz
- Microbiology Program, School of Biological Sciences, Southern Illinois University, Carbondale, IL, USA
| | - Neil Billington
- Cell Biology and Physiology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Ian Seim
- Biology Department, University of North Carolina, Chapel Hill, NC, USA
- Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, NC, USA
- Curriculum in Bioinformatics and Computational Biology, University of North Carolina, Chapel Hill, NC, USA
| | - Joanne Ekena
- Biology Department, University of North Carolina, Chapel Hill, NC, USA
| | - James R. Sellers
- Cell Biology and Physiology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Amy. S. Gladfelter
- Biology Department, University of North Carolina, Chapel Hill, NC, USA
- Marine Biological Laboratory, Woods Hole, MA, USA
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2
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Woods BL, Cannon KS, Vogt EJD, Crutchley JM, Gladfelter AS. Interplay of septin amphipathic helices in sensing membrane-curvature and filament bundling. Mol Biol Cell 2021; 32:br5. [PMID: 34319771 PMCID: PMC8684760 DOI: 10.1091/mbc.e20-05-0303] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The curvature of the membrane defines cell shape. Septins are GTP-binding proteins that assemble into heteromeric complexes and polymerize into filaments at areas of micron-scale membrane curvature. An amphipathic helix (AH) domain within the septin complex is necessary and sufficient for septins to preferentially assemble onto micron-scale curvature. Here we report that the nonessential fungal septin, Shs1, also has an AH domain capable of recognizing membrane curvature. In a septin mutant strain lacking a fully functional Cdc12 AH domain (cdc12-6), the C-terminal extension of Shs1, containing an AH domain, becomes essential. Additionally, we find that the Cdc12 AH domain is important for regulating septin filament bundling, suggesting septin AH domains have multiple, distinct functions and that bundling and membrane binding may be coordinately controlled.
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Affiliation(s)
- Benjamin L Woods
- Biology Department, University of North Carolina, Chapel Hill, NC 27599
| | - Kevin S Cannon
- Biology Department, University of North Carolina, Chapel Hill, NC 27599
| | - Ellysa J D Vogt
- Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599
| | - John M Crutchley
- Biology Department, University of North Carolina, Chapel Hill, NC 27599
| | - Amy S Gladfelter
- Biology Department, University of North Carolina, Chapel Hill, NC 27599.,Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599.,Marine Biological Laboratory, Woods Hole, MA 02543
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Szuba A, Bano F, Castro-Linares G, Iv F, Mavrakis M, Richter RP, Bertin A, Koenderink GH. Membrane binding controls ordered self-assembly of animal septins. eLife 2021; 10:63349. [PMID: 33847563 PMCID: PMC8099429 DOI: 10.7554/elife.63349] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Accepted: 04/12/2021] [Indexed: 12/23/2022] Open
Abstract
Septins are conserved cytoskeletal proteins that regulate cell cortex mechanics. The mechanisms of their interactions with the plasma membrane remain poorly understood. Here, we show by cell-free reconstitution that binding to flat lipid membranes requires electrostatic interactions of septins with anionic lipids and promotes the ordered self-assembly of fly septins into filamentous meshworks. Transmission electron microscopy reveals that both fly and mammalian septin hexamers form arrays of single and paired filaments. Atomic force microscopy and quartz crystal microbalance demonstrate that the fly filaments form mechanically rigid, 12- to 18-nm thick, double layers of septins. By contrast, C-terminally truncated septin mutants form 4-nm thin monolayers, indicating that stacking requires the C-terminal coiled coils on DSep2 and Pnut subunits. Our work shows that membrane binding is required for fly septins to form ordered arrays of single and paired filaments and provides new insights into the mechanisms by which septins may regulate cell surface mechanics.
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Affiliation(s)
- Agata Szuba
- AMOLF, Department of Living Matter, Biological Soft Matter group, Amsterdam, Netherlands
| | - Fouzia Bano
- School of Biomedical Sciences, Faculty of Biological Sciences, Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Physics and Astronomy, Faculty of Engineering and Physical Sciences, University of Leeds, Leeds, United Kingdom.,Bragg Centre for Materials Research, University of Leeds, Leeds, United Kingdom
| | - Gerard Castro-Linares
- AMOLF, Department of Living Matter, Biological Soft Matter group, Amsterdam, Netherlands.,Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands
| | - Francois Iv
- Institut Fresnel, CNRS, Aix-Marseille Univ, Centrale Marseille, Marseille, France
| | - Manos Mavrakis
- Institut Fresnel, CNRS, Aix-Marseille Univ, Centrale Marseille, Marseille, France
| | - Ralf P Richter
- School of Biomedical Sciences, Faculty of Biological Sciences, Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Physics and Astronomy, Faculty of Engineering and Physical Sciences, University of Leeds, Leeds, United Kingdom.,Bragg Centre for Materials Research, University of Leeds, Leeds, United Kingdom
| | - Aurélie Bertin
- Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, Paris, France.,Sorbonne Université, Paris, France
| | - Gijsje H Koenderink
- AMOLF, Department of Living Matter, Biological Soft Matter group, Amsterdam, Netherlands.,Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands
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Cannon KS, Woods BL, Crutchley JM, Gladfelter AS. An amphipathic helix enables septins to sense micrometer-scale membrane curvature. J Cell Biol 2019; 218:1128-1137. [PMID: 30659102 PMCID: PMC6446858 DOI: 10.1083/jcb.201807211] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 11/17/2018] [Accepted: 01/07/2019] [Indexed: 02/04/2023] Open
Abstract
The basis of curvature sensing by the septin cytoskeleton is unknown. Cannon et al. now identify a conserved amphipathic helix that is necessary for recruitment of septins to sites of micrometer-scale curvature in vitro and in vivo. Cell shape is well described by membrane curvature. Septins are filament-forming, GTP-binding proteins that assemble on positive, micrometer-scale curvatures. Here, we examine the molecular basis of curvature sensing by septins. We show that differences in affinity and the number of binding sites drive curvature-specific adsorption of septins. Moreover, we find septin assembly onto curved membranes is cooperative and show that geometry influences higher-order arrangement of septin filaments. Although septins must form polymers to stay associated with membranes, septin filaments do not have to span micrometers in length to sense curvature, as we find that single-septin complexes have curvature-dependent association rates. We trace this ability to an amphipathic helix (AH) located on the C-terminus of Cdc12. The AH domain is necessary and sufficient for curvature sensing both in vitro and in vivo. These data show that curvature sensing by septins operates at much smaller length scales than the micrometer curvatures being detected.
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Affiliation(s)
- Kevin S Cannon
- Department of Biology, University of North Carolina at Chapel Hill, NC
| | - Benjamin L Woods
- Department of Biology, University of North Carolina at Chapel Hill, NC
| | - John M Crutchley
- Department of Biology, University of North Carolina at Chapel Hill, NC
| | - Amy S Gladfelter
- Department of Biology, University of North Carolina at Chapel Hill, NC .,Marine Biological Laboratory, Woods Hole, MA
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Momany M, Talbot NJ. Septins Focus Cellular Growth for Host Infection by Pathogenic Fungi. Front Cell Dev Biol 2017; 5:33. [PMID: 28424773 PMCID: PMC5380669 DOI: 10.3389/fcell.2017.00033] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2016] [Accepted: 03/21/2017] [Indexed: 11/13/2022] Open
Abstract
One of the key challenges faced by microbial pathogens is invasion of host tissue. Fungal pathogens adopt a number of distinct strategies to overcome host cell defenses, including the development of specialized infection structures, the secretion of proteins that manipulate host responses or cellular organization, and the ability to facilitate their own uptake by phagocytic mechanisms. Key to many of these adaptations is the considerable morphogenetic plasticity displayed by pathogenic species. Fungal pathogens can, for example, shift their growth habit between non-polarized spores, or yeast-like cells, and highly polarized hyphal filaments. These polarized filaments can then elaborate differentiated cells, specialized to breach host barriers. Septins play fundamental roles in the ability of diverse fungi to undergo shape changes and organize the F-actin cytoskeleton to facilitate invasive growth. As a consequence, septins are increasingly implicated in fungal pathogenesis, with many septin mutants displaying impairment in their ability to cause diseases of both plants and animals. In this mini-review, we show that a common feature of septin mutants is the emergence of extra polar outgrowths during morphological transitions, such as emergence of germ tubes from conidia or branches from hyphae. We propose that because septins detect and stabilize membrane curvature, they prevent extra polar outgrowths and thereby focus fungal invasive force, allowing substrate invasion.
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Affiliation(s)
- Michelle Momany
- Department of Plant Biology, University of GeorgiaAthens, OH, USA
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Torraca V, Mostowy S. Septins and Bacterial Infection. Front Cell Dev Biol 2016; 4:127. [PMID: 27891501 PMCID: PMC5104955 DOI: 10.3389/fcell.2016.00127] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 10/26/2016] [Indexed: 12/04/2022] Open
Abstract
Septins, a unique cytoskeletal component associated with cellular membranes, are increasingly recognized as having important roles in host defense against bacterial infection. A role for septins during invasion of Listeria monocytogenes into host cells was first proposed in 2002. Since then, work has shown that septins assemble in response to a wide variety of invasive bacterial pathogens, and septin assemblies can have different roles during the bacterial infection process. Here we review the interplay between septins and bacterial pathogens, highlighting septins as a structural determinant of host defense. We also discuss how investigation of septin assembly in response to bacterial infection can yield insight into basic cellular processes including phagocytosis, autophagy, and mitochondrial dynamics.
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Affiliation(s)
- Vincenzo Torraca
- Department of Medicine, MRC Centre of Molecular Bacteriology and Infection, Imperial College London London, UK
| | - Serge Mostowy
- Department of Medicine, MRC Centre of Molecular Bacteriology and Infection, Imperial College London London, UK
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