A peptide methionine sulfoxide reductase highly expressed in photosynthetic tissue in Arabidopsis thaliana can protect the chaperone-like activity of a chloroplast-localized small heat shock protein.

• The oxidation of methionine residues in proteins to methionine sulfoxides occurs frequently and protein repair by reduction of the methionine sulfoxides is mediated by an enzyme, peptide methionine sulfoxide reductase (PMSR, EC 1.8.4.6), universally present in the genomes of all so far sequenced organisms. Recently, five PMSR-like genes were identified in Arabidopsis thaliana, including one plastidic isoform, chloroplast localised plastidial peptide methionine sulfoxide reductase (pPMSR) that was chloroplast-localized and highly expressed in actively photosynthesizing tissue (Sadanandom A et al., 2000). However, no endogenous substrate to the pPMSR was identified. Here we report that a set of highly conserved methionine residues in Hsp21, a chloroplast-localized small heat shock protein, can become sulfoxidized and thereafter reduced back to methionines by this pPMSR. The pPMSR activity was evaluated using recombinantly expressed pPMSR and Hsp21 from Arabidopsis thaliana and a direct detection of methionine sulfoxides in Hsp21 by mass spectrometry. The pPMSR-catalyzed reduction of Hsp21 methionine sulfoxides occurred on a minute time-scale, was ultimately DTT-dependent and led to recovery of Hsp21 conformation and chaperone-like activity, both of which are lost upon methionine sulfoxidation (Härndahl et al., 2001). These data indicate that one important function of pPMSR may be to prevent inactivation of Hsp21 by methionine sulfoxidation, since small heat shock proteins are crucial for cellular resistance to oxidative stress.

Subject headings

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Keyword

Plant Leaves/*enzymology/genetics

Oxidoreductases/genetics/*metabolism

Oxidative Stress

Oxidation-Reduction/drug effects

Mutation

Site-Directed

Mutagenesis

Molecular Chaperones/genetics/metabolism

Methionine/*analogs & derivatives/metabolism

Isoenzymes/genetics/metabolism

Heat-Shock Proteins/genetics/*metabolism

Gene Expression

Escherichia coli/genetics

Dithiothreitol/pharmacology

Citrate (si)-Synthase/metabolism

Arabidopsis/*enzymology/genetics

Chloroplasts/enzymology/metabolism

Plastids/enzymology

Recombinant Proteins/metabolism

Spectrometry

Mass

Matrix-Assisted Laser Desorption-Ionization

Support

Non-U.S. Gov't

Publication and Content Type

art (subject category)

ref (subject category)