Heat shock protein (hsp90) interacts with smooth muscle calponin and affects calponin-binding to actin

Interaction of smooth muscle calponin with 90 kDa heat shock protein (hsp90 ) was analyzed by means of native gel electrophoresis and affinity chromato graphy. Under conditions used, calponin and hsp90 form a complex with an ap parent dissociation constant in the micromolar range. The major hsp90-bindi ng site is located in the N-terminal (residues 7-144) part of calponin. Add ition of calponin to actin-tropomyosin complex results in formation of acti n bundles. Hsp90 partially prevents bundle formation without affecting the molar ratio calponin/actin in single actin filaments or actin bundles. At l ow ionic strength, calponin induces polymerization of G-actin. Hsp90 decrea ses calponin-induced polymerization of G-actin. It is supposed that hsp90 m ay be involved in the assembly of actin filaments. (C) 2000 Elsevier Scienc e B.V. All rights reserved.