The chaperone-like activity of a small heat shock protein is lost after sulfoxidation of conserved methionines in a surface-exposed amphipathic alpha-helix.
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.
Härndahl
U
U
Department of Biochemistry, Lund University, Sweden.
Kokke
B P
BP
Gustavsson
N
N
Linse
S
S
Berggren
K
K
Tjerneld
F
F
Boelens
W C
WC
Sundby
C
C
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins; D002736:Chloroplasts / Q000737:chemistry; D002850:Chromatography, Gel; D002942:Circular Dichroism; D002950:Citrate (si)-Synthase / Q000737:chemistry; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000502:physiology; D007328:Insulin / Q000737:chemistry; D008715:Methionine / Q000737:chemistry; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010449:Peptide Mapping; D010940:Plant Proteins / Q000737:chemistry* / Q000502:physiology; D011487:Protein Conformation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013455:Sulfur / Q000378:metabolism*; D013816:Thermodynamics
D029681:Arabidopsis Proteins; C400143:HSP21 protein, Arabidopsis; D006360:Heat-Shock Proteins; D007328:Insulin; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D013455:Sulfur; D008715:Methionine; D002950:Citrate (si)-Synthase