title: Structural basis for ESCRT-III protein autoinhibition.
abstract: Endosomal sorting complexes required for transport-III (ESCRT-III) subunits cycle between two states: soluble monomers and higher-order assemblies that bind and remodel membranes during endosomal vesicle formation, midbody abscission and enveloped virus budding. Here we show that the N-terminal core domains of increased sodium tolerance-1 (IST1) and charged multivesicular body protein-3 (CHMP3) form equivalent four-helix bundles, revealing that IST1 is a previously unrecognized ESCRT-III family member. IST1 and its ESCRT-III binding partner, CHMP1B, both form higher-order helical structures in vitro, and IST1-CHMP1 interactions are required for abscission. The IST1 and CHMP3 structures also reveal that equivalent downstream alpha5 helices can fold back against the core domains. Mutations within the CHMP3 core-alpha5 interface stimulate the protein's in vitro assembly and HIV-inhibition activities, indicating that dissociation of the autoinhibitory alpha5 helix from the core activates ESCRT-III proteins for assembly at membranes.
authors.affiliation: Department of Biochemistry, University of Utah, Salt Lake City, Utah, USA.
authors.forename: Monika
authors.initials: M
authors.lastname: Bajorek
authors.forename: Heidi L
authors.initials: HL
authors.lastname: Schubert
authors.forename: John
authors.initials: J
authors.lastname: McCullough
authors.forename: Charles
authors.initials: C
authors.lastname: Langelier
authors.forename: Debra M
authors.initials: DM
authors.lastname: Eckert
authors.forename: William-May B
authors.initials: WM
authors.lastname: Stubblefield
authors.forename: Nathan T
authors.initials: NT
authors.lastname: Uter
authors.forename: David G
authors.initials: DG
authors.lastname: Myszka
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Hill
authors.forename: Wesley I
authors.initials: WI
authors.lastname: Sundquist
mesh_terms: D018360:Crystallography, X-Ray; D048749:Cytokinesis / Q000502:physiology; D019281:Dimerization; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D015513:Oncogene Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: C541483:CHMP1B protein, human; C498543:CHMP3 protein, human; D056827:Endosomal Sorting Complexes Required for Transport; C533705:IST1 protein, human; D046912:Multiprotein Complexes; D015513:Oncogene Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D033921:Vesicular Transport Proteins