Subunit arrangement in the dodecameric chloroplast small heat shock protein Hsp21 |
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| Authors: | Lambert Wietske Koeck Philip J B Ahrman Emma Purhonen Pasi Cheng Kimberley Elmlund Dominika Hebert Hans Emanuelsson Cecilia |
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| Institution: | 1Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, Sweden;2Department of Bioscience, Karolinska Institutet, Novum, Sweden |
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| 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. |
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| Keywords: | chloroplast heat shock protein image reconstruction mass spectrometry protein crosslinking protein structure protein–protein interactions single particle electron microscopy plant stress response structural mapping |
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