title: An intermediate structure in the thermal unfolding of the GTPase domain of human septin 4 (SEPT4/Bradeion-beta) forms amyloid-like filaments in vitro.
abstract: SEPT4 is a member of the mammalian septin family of GTPases. Mammalian septins are conserved proteins which form heteropolymers in vivo and which are implicated in a variety of cellular functions such as cytokinesis, exocytosis, and vesicle trafficking. However, their structural properties and modes of action are largely unknown. There is a limited, but as yet inconclusive, amount of experimental data suggesting that SEPT4 may accumulate in tau-based filamentous deposits and cytoplasmic inclusions in Alzheimer's and Parkinson's disease, respectively. Here we report an intermediate structure of the GTPase domain of human SEPT4 (SEPT4-G) during unfolding transitions induced by temperature. This partially unfolded intermediate, which is rich in beta-sheet and free of bound nucleotide, was plagued by irreversible aggregation. The aggregates have the ability to bind specific dyes such as Congo red and thioflavin-T, suggesting they are amyloid in nature. Under electron microscopy, fibers of variable diameter extending for several micrometers in length can be visualized. This is the first report of amyloid formation by a septin or domain thereof, and the capacity of SEPT4-G to form such fibrillar aggregates may shed some light on the current discussion concerning the formation of homo- and heteropolymers of septins in vitro.
authors.affiliation: Centro de Biotecnologia Molecular e Estrutural, Instituto de Física de São Carlos, Universidade de São Paulo, São Paulo, Brazil. wanius@if.sc.usp.br
authors.forename: Wanius
authors.initials: W
authors.lastname: Garcia
authors.forename: Ana Paula Ulian
authors.initials: AP
authors.lastname: de Araújo
authors.forename: Flavio
authors.initials: F
authors.lastname: Lara
authors.forename: Debora
authors.initials: D
authors.lastname: Foguel
authors.forename: Manami
authors.initials: M
authors.lastname: Tanaka
authors.forename: Tomoo
authors.initials: T
authors.lastname: Tanaka
authors.forename: Richard Charles
authors.initials: RC
authors.lastname: Garratt
mesh_terms: D000682:Amyloid / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003224:Congo Red / Q000737:chemistry; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D006358:Hot Temperature; D006801:Humans; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D008956:Models, Chemical; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D058112:Septins; D044366:Transition Temperature
chemical_list: D000682:Amyloid; D003598:Cytoskeletal Proteins; D011994:Recombinant Proteins; D003224:Congo Red; D020558:GTP Phosphohydrolases; C492027:SEPTIN4 protein, human; D058112:Septins