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Structure. 2006 Jul;14(7):1197-204.

Multiple distinct assemblies reveal conformational flexibility in the small heat shock protein Hsp26.

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  • 1Department of Crystallography, Birkbeck College, London WC1E 7HX, United Kingdom.


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.

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