Subunit arrangement in the dodecameric chloroplast small heat shock protein Hsp21

Wietske Lambert, Philip J B Koeck, Emma Ahrman, Pasi Purhonen, Kimberley Cheng, Dominika Elmlund, Hans Hebert, Cecilia Emanuelsson

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Unfolding proteins are prevented from irreversible aggregation by small heat shock proteins (sHsps) through interactions that depend on a dynamic equilibrium between sHsp subunits and sHsp oligomers. A chloroplast-localized sHsp, Hsp21, provides protection to client proteins to increase plant stress resistance. Structural information is lacking concerning the oligomeric conformation of this sHsp. We here present a structure model of Arabidopsis thaliana Hsp21, obtained by homology modeling, single-particle electron microscopy, and lysine-specific chemical crosslinking. The model shows that the Hsp21 subunits are arranged in two hexameric discs, similar to a cytosolic plant sHsp homolog that has been structurally determined after crystallization. However, the two hexameric discs of Hsp21 are rotated by 25° in relation to each other, suggesting a role for global dynamics in dodecamer function. Published by Wiley-Blackwell.

Original languageEnglish
Pages (from-to)291-301
Number of pages11
JournalProtein Science
Issue number2
Publication statusPublished - Feb 2011
Externally publishedYes


  • Chloroplast
  • Heat shock protein
  • Image reconstruction
  • Mass spectrometry
  • Plant stress response
  • Protein crosslinking
  • Protein structure
  • Protein-protein interactions
  • Single particle electron microscopy
  • Structural mapping

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