title: The hexameric structure of the human mitochondrial replicative helicase Twinkle.
abstract: The mitochondrial replicative helicase Twinkle is involved in strand separation at the replication fork of mitochondrial DNA (mtDNA). Twinkle malfunction is associated with rare diseases that include late onset mitochondrial myopathies, neuromuscular disorders and fatal infantile mtDNA depletion syndrome. We examined its 3D structure by electron microscopy (EM) and small angle X-ray scattering (SAXS) and built the corresponding atomic models, which gave insight into the first molecular architecture of a full-length SF4 helicase that includes an N-terminal zinc-binding domain (ZBD), an intermediate RNA polymerase domain (RPD) and a RecA-like hexamerization C-terminal domain (CTD). The EM model of Twinkle reveals a hexameric two-layered ring comprising the ZBDs and RPDs in one layer and the CTDs in another. In the hexamer, contacts in trans with adjacent subunits occur between ZBDs and RPDs, and between RPDs and CTDs. The ZBDs show important structural heterogeneity. In solution, the scattering data are compatible with a mixture of extended hexa- and heptameric models in variable conformations. Overall, our structural data show a complex network of dynamic interactions that reconciles with the structural flexibility required for helicase activity.
authors.affiliation: Structural MitoLab; Department of Structural Biology, Molecular Biology Institute Barcelona (IBMB-CSIC), Barcelona, E-08028, Spain.
authors.forename: Pablo
authors.identifier: http://orcid.org/0000-0002-7402-4983
authors.initials: P
authors.lastname: Fernández-Millán
authors.affiliation: Structural Biology Unit. Centre for Cooperative Research in Biosciences, CICbioGUNE, Derio, E-48160, Spain.
authors.forename: Melisa
authors.identifier: http://orcid.org/0000-0002-9603-9115
authors.initials: M
authors.lastname: Lázaro
authors.affiliation: Department of Pediatrics, Nijmegen Centre for Mitochondrial Disorders, Radboud University Medical Centre, Nijmegen, 6525 GA, The Netherlands.
authors.forename: Şirin
authors.initials: Ş
authors.lastname: Cansız-Arda
authors.affiliation: Department of Pediatrics, Nijmegen Centre for Mitochondrial Disorders, Radboud University Medical Centre, Nijmegen, 6525 GA, The Netherlands.
authors.forename: Joachim M
authors.identifier: http://orcid.org/0000-0002-4972-1947
authors.initials: JM
authors.lastname: Gerhold
authors.affiliation: Mitochondrial DNA Maintenance Group, BioMediTech, University of Tampere, Tampere, FI-33014, Finland.
authors.forename: Nina
authors.initials: N
authors.lastname: Rajala
authors.affiliation: Structural MitoLab; Department of Structural Biology, Molecular Biology Institute Barcelona (IBMB-CSIC), Barcelona, E-08028, Spain.
authors.forename: Claus-A
authors.initials: CA
authors.lastname: Schmitz
authors.affiliation: Structural MitoLab; Department of Structural Biology, Molecular Biology Institute Barcelona (IBMB-CSIC), Barcelona, E-08028, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Silva-Espiña
authors.affiliation: Structural Biology Unit. Centre for Cooperative Research in Biosciences, CICbioGUNE, Derio, E-48160, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Gil
authors.affiliation: Centre de Biochimie Structurale, INSERM-U1054, CNRS UMR-5048, Université de Montpellier I&II. Montpellier, F-34090, France.
authors.forename: Pau
authors.identifier: http://orcid.org/0000-0001-7395-5922
authors.initials: P
authors.lastname: Bernadó
authors.affiliation: Structural Biology Unit. Centre for Cooperative Research in Biosciences, CICbioGUNE, Derio, E-48160, Spain mvalle@cicbiogune.es.
authors.forename: Mikel
authors.identifier: http://orcid.org/0000-0001-8268-6912
authors.initials: M
authors.lastname: Valle
authors.affiliation: Department of Pediatrics, Nijmegen Centre for Mitochondrial Disorders, Radboud University Medical Centre, Nijmegen, 6525 GA, The Netherlands Mitochondrial DNA Maintenance Group, BioMediTech, University of Tampere, Tampere, FI-33014, Finland hans.spelbrink@radboudumc.nl.
authors.forename: Johannes N
authors.initials: JN
authors.lastname: Spelbrink
authors.affiliation: Structural MitoLab; Department of Structural Biology, Molecular Biology Institute Barcelona (IBMB-CSIC), Barcelona, E-08028, Spain maria.sola@ibmb.csic.es.
authors.forename: Maria
authors.initials: M
authors.lastname: Solà
mesh_terms: D004265:DNA Helicases / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D006801:Humans; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D008958:Models, Molecular; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D040681:Structural Homology, Protein; D014961:X-Ray Diffraction
chemical_list: D024101:Mitochondrial Proteins; D004265:DNA Helicases; C431576:TWNK protein, human
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