Conserved methionines in chloroplasts

Cecilia Sundby*, Ulrika Härndahl, Niklas Gustavsson, Emma Åhrman, Denis J. Murphy

*Corresponding author for this work

    Research output: Contribution to journalReview articlepeer-review

    35 Citations (Scopus)


    Heat shock proteins counteract heat and oxidative stress. In chloroplasts, a small heat shock protein (Hsp21) contains a set of conserved methionines, which date back to early in the emergence of terrestrial plants. Methionines M49, M52, M55, M59, M62, M67 are located on one side of an amphipathic helix, which may fold back over two other conserved methionines (M97 and M101), to form a binding groove lined with methionines, for sequence-independent recognition of peptides with an overall hydrophobic character. The sHsps protect other proteins from aggregation by binding to their hydrophobic surfaces, which become exposed under stress. Data are presented showing that keeping the conserved methionines in Hsp21 in a reduced form is a prerequisite to maintain such binding. The chloroplast generates reactive oxygen species under both stress and unstressed conditions, but this organelle is also a highly reducing cellular compartment. Chloroplasts contain a specialized isoform of the enzyme, peptide methionine sulfoxide reductase, the expression of which is light-induced. Recombinant proteins were used to measure that this reductase can restore Hsp21 methionines after sulfoxidation. This paper also describes how methionine sulfoxidation-reduction can be directly assessed by mass spectrometry, how methionine-to-leucine substitution affects Hsp21, and discusses the possible role for an Hsp21 methionine sulfoxidation-reduction cycle in quenching reactive oxygen species.

    Original languageEnglish
    Pages (from-to)191-202
    Number of pages12
    JournalBiochimica et Biophysica Acta - Proteins and Proteomics
    Issue number2
    Publication statusPublished - 17 Jan 2005


    • Chaperone
    • Heat stress
    • Oxidative stress
    • Photosynthesis
    • Protein mass spectrometry
    • Protein-protein interaction


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