MOLECULAR CHAPERONE MACHINES - CHAPERONE ACTIVITIES OF THE CYCLOPHILIN CYP-40 AND THE STEROID APORECEPTOR-ASSOCIATED PROTEIN P23

Molecular chaperones are essential proteins that participate in the re gulation of steroid receptors in eukaryotes. The steroid aporeceptor c omplex contains the molecular chaperones Hsp90 and Hsp70, p48, the cyc lophilin Cyp-40, and the associated proteins p23 and p60. In vitro fol ding assays showed that Cyp-40 and p23 functioned as molecular chapero nes in a manner similar to that of Hsp90 or Hsp70. Although neither Cy p-40 nor p23 could completely refold an unfolded substrate, both prote ins interacted with the substrate to maintain a nonnative folding-comp etent intermediate. Thus, the steroid aporeceptor complexes have multi ple chaperone components that maintain substrates in an intermediate f olded state.