Localization of calponin binding sites in the structure of 90 kDa heat shock protein (Hsp90)

The structure of rabbit liver Hsp90 was reevaluated by limited trypsinolysis, N-terminal sequencing and determination of the site that is phosphorylated by casein kinase II. Limited proteolysis results in formation of four groups of large peptides with Mr in the range of 26–41 kDa. Peptides with Mr 39–41 kDa were represented by large N-terminal and central peptides starting at residue 283 of the α-isoform of Hsp90. All sites phosphorylated by casein kinase II were located in the large 39–41 kDa peptides. Peptides with Mr 26–27 kDa were represented by short N-terminal and central peptides starting at Glu-400 of the α-isoform of Hsp90. The data of affinity chromatography and light scattering indicate that smooth muscle calponin interacts with Hsp90. The calponin binding sites are located in the large (37–41 kDa) N-terminal and in a short (26–27 kDa) central peptide starting at Glu-400 of the α-isoform of Hsp90. Phosphorylation by casein kinase II up to 2 mol of phosphate per mol of Hsp90 does not affect interaction of Hsp90 with calponin.