title: Multiple distinct assemblies reveal conformational flexibility in the small heat shock protein Hsp26.
abstract: Small heat shock proteins are a superfamily of molecular chaperones that suppress protein aggregation and provide protection from cell stress. A key issue for understanding their action is to define the interactions of subunit domains in these oligomeric assemblies. Cryo-electron microscopy of yeast Hsp26 reveals two distinct forms, each comprising 24 subunits arranged in a porous shell with tetrahedral symmetry. The subunits form elongated, asymmetric dimers that assemble via trimeric contacts. Modifications of both termini cause rearrangements that yield a further four assemblies. Each subunit contains an N-terminal region, a globular middle domain, the alpha-crystallin domain, and a C-terminal tail. Twelve of the C termini form 3-fold assembly contacts which are inserted into the interior of the shell, while the other 12 C termini form contacts on the surface. Hinge points between the domains allow a variety of assembly contacts, providing the flexibility required for formation of supercomplexes with non-native proteins.
authors.affiliation: Department of Crystallography, Birkbeck College, London WC1E 7HX, United Kingdom.
authors.forename: Helen E
authors.initials: HE
authors.lastname: White
authors.forename: Elena V
authors.initials: EV
authors.lastname: Orlova
authors.forename: Shaoxia
authors.initials: S
authors.lastname: Chen
authors.forename: Luchun
authors.initials: L
authors.lastname: Wang
authors.forename: Athanasios
authors.initials: A
authors.lastname: Ignatiou
authors.forename: Brent
authors.initials: B
authors.lastname: Gowen
authors.forename: Thusnelda
authors.initials: T
authors.lastname: Stromer
authors.forename: Titus M
authors.initials: TM
authors.lastname: Franzmann
authors.forename: Martin
authors.initials: M
authors.lastname: Haslbeck
authors.forename: Johannes
authors.initials: J
authors.lastname: Buchner
authors.forename: Helen R
authors.initials: HR
authors.lastname: Saibil
mesh_terms: D001665:Binding Sites; D020285:Cryoelectron Microscopy; D019281:Dimerization; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D020836:Protein Structure, Quaternary; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D038201:alpha-Crystallins / Q000737:chemistry
chemical_list: C499528:HSP26 protein, S cerevisiae; D006360:Heat-Shock Proteins; D029701:Saccharomyces cerevisiae Proteins; D038201:alpha-Crystallins