Figure 1. Interaction between calpain and HSP90.

(A) Purified calpain-1 or-2 (1.5 µg) was incubated for 1 hour at 25°C with the indicated amounts of purified HSP90. Immunoprecipitation was carried out using 1 µg of anti-HSP90 antibody. Immunoprecipitated material (IP HSP90) was submitted to SDS-PAGE and analysed by immunoblotting using monoclonal anti-calpain-1 (○) or anti-calpain-2 (■). Inset: a representative blot for calpain-1 is shown. (B) Alternatively, HSP90 (3 µg) was incubated for 1 hour at 25°C with the indicated amounts of purified calpain-1. Immunoprecipitated material (IP Calpain-1), obtained using 1 µg of monoclonal anti-calpain-1, was submitted to SDS-PAGE and analysed by immunoblotting using monoclonal anti-HSP90. Inset: a representative blot is shown. Immunoprecipitations were also performed in the presence of 1 mM CaCl₂ and 100 µg/mL leupeptin (Δ). Each point corresponds to the arithmetic mean ± SD of five different experiments.