Purification and characterization of two small heat shock proteins from Anabaena sp. PCC 7120

Two small heat shock proteins (sHsps), Hsp17.8 and Hsp17.1, were identified in the cyanobacterium Anabaena sp. PCC 7120. Recombinant Hsp17.8 and Hsp17.1 were overexpressed in Escherichia coli and characterized here. Hsp17.8 was purified by sequential chromatography on DEAE-Sepharose and Superose 6 10/300 column, and Hsp17.1 was purified by Superose 6 10/300 column in 4M urea. Size exclusion chromatography demonstrated that both purified proteins form large oligomers approximately 420kDa and 410kDa, respectively. Both Hsp17.8 and Hsp17.1 showed chaperone-like activity to protect citrate synthase (CS) from thermal aggregation at 43 degrees C. Furthermore, both proteins were found to form complexes with denatured CS at 45 degrees C. Our study also demonstrated that despite a high degree of sequence homology and similar subunit size, Hsp17.1 showed higher hydrophobicity indicated by 8-anilino-1-naphthalene sulfonate fluorescence and thus greater chaperone-like activity. This is the first report of characterization and comparison of an sHsp system containing two chaperones in cyanobacteria.