title: Subunit arrangement in the dodecameric chloroplast small heat shock protein Hsp21.
abstract: 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.
authors.affiliation: Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, Sweden. wietske.lambert@biochemistry.lu.se
authors.forename: Wietske
authors.initials: W
authors.lastname: Lambert
authors.forename: Philip J B
authors.initials: PJ
authors.lastname: Koeck
authors.forename: Emma
authors.initials: E
authors.lastname: Ahrman
authors.forename: Pasi
authors.initials: P
authors.lastname: Purhonen
authors.forename: Kimberley
authors.initials: K
authors.lastname: Cheng
authors.forename: Dominika
authors.initials: D
authors.lastname: Elmlund
authors.forename: Hans
authors.initials: H
authors.lastname: Hebert
authors.forename: Cecilia
authors.initials: C
authors.lastname: Emanuelsson
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D002736:Chloroplasts / Q000737:chemistry*; D003432:Cross-Linking Reagents; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D008239:Lysine / Q000737:chemistry / Q000378:metabolism; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D055503:Protein Multimerization; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D040681:Structural Homology, Protein
chemical_list: D029681:Arabidopsis Proteins; D003432:Cross-Linking Reagents; C400143:HSP21 protein, Arabidopsis; D006360:Heat-Shock Proteins; D021122:Protein Subunits; D008239:Lysine