The chaperone-like activity of a small heat shock protein is lost after sulfoxidation of conserved methionines in a surface-exposed amphipathic alpha-helix

Biochim Biophys Acta. 2001 Feb 9;1545(1-2):227-37. doi: 10.1016/s0167-4838(00)00280-6.


The small heat shock proteins (sHsps) possess a chaperone-like activity which prevents aggregation of other proteins during transient heat or oxidative stress. The sHsps bind, onto their surface, molten globule forms of other proteins, thereby keeping them in a refolding competent state. In Hsp21, a chloroplast-located sHsp in all higher plants, there is a highly conserved region forming an amphipathic alpha-helix with several methionines on the hydrophobic side according to secondary structure prediction. This paper describes how sulfoxidation of the methionines in this amphipathic alpha-helix caused conformational changes and a reduction in the Hsp21 oligomer size, and a complete loss of the chaperone-like activity. Concomitantly, there was a loss of an outer-surface located alpha-helix as determined by limited proteolysis and circular dichroism spectroscopy. The present data indicate that the methionine-rich amphipathic alpha-helix, a motif of unknown physiological significance which evolved during the land plant evolution, is crucial for binding of substrate proteins and has rendered the chaperone-like activity of Hsp21 very dependent on the chloroplast redox state.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / metabolism
  • Arabidopsis Proteins
  • Chloroplasts / chemistry
  • Chromatography, Gel
  • Circular Dichroism
  • Citrate (si)-Synthase / chemistry
  • Heat-Shock Proteins / chemistry*
  • Heat-Shock Proteins / physiology
  • Insulin / chemistry
  • Methionine / chemistry
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Oxidative Stress
  • Peptide Mapping
  • Plant Proteins / chemistry*
  • Plant Proteins / physiology
  • Protein Conformation
  • Protein Folding
  • Protein Processing, Post-Translational*
  • Recombinant Fusion Proteins / chemistry
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Sulfur / metabolism*
  • Thermodynamics


  • Arabidopsis Proteins
  • HSP21 protein, Arabidopsis
  • Heat-Shock Proteins
  • Insulin
  • Plant Proteins
  • Recombinant Fusion Proteins
  • Sulfur
  • Methionine
  • Citrate (si)-Synthase