The Chloroplast Small Heat Shock Protein Studied by Peptide Mapping and Mass Spectrometry Using Purified Recombinant Protein From Arabidopsis Thaliana and Pea

Abstract

By using peptide mapping and mass spectrometry, we have studied how the purified, recombinant HSP21 oligomer is affected by oxidative stress. The chloroplast small heat shock protein HSP21 is nuclear encoded and a member of the evolutionary well conserved family of small heat shock proteins (sHSPs) [1]. The sHSPs are considered to confer thermotolerance and specific roles of the sHSPs have been proposed such as protection of photosystem II and mRNA [2–4]. Also some sHSPs prevent aggregation of proteins during heat stress in vitro in a chaperone-like manner [5, 6]. However, the functional mechanisms by which HSP21 confers thermotolerance remains to be solved. HSP21 is assembled into oligomers of approximately 230 and 300 kDa for pea and Arabidopsis thaliana (At), respectively. We have found that purified recombinant HSP21 oligomer undergoes conformational changes which mimic changes occuring in heat stressed plants [Härndahl et al., these proceedings], which probably involve temperature dependent oxidation.