Binding of Immunophilins to the 90 kDa Heat Shock Protein (hsp90) via a Tetratricopeptide Repeat Domain Is a Conserved Protein Interaction in Plants

摘要

In animal cell lysates, multiprotein complexes containing hsp90, hsp70, p60, p23, and several immunophilins can assemble steroid receptors and oncogenic protein kinases, such as v-Src and v-Raf, into heterocomplexes that contain hsp90 and either immunophilins or, in the case of protein kinases, p50. The complexes with hsp90 are required for the proper functioning of these signal transduction systems. Wheat germ lysate contains a similar protein folding activity that forms functional steroid receptorcomplexes with hsp90, but not all the components of this system have been identified. The plant chaperone system has conserved interactions with animal chaperones in that wheat hsp70 functions in the rabbit reticulocyte lysate heterocomplex assembly system and human p23 functions in the wheat germ lysate. Here, we ask if wheat germ lysate also contains immunophilins of the FK506-binding class (FKBPs) that bind to the hsp90 component of the ehaperone complex via tetratricopeptide repeat (TPR) domains. Todemonstrate the plant heterocomplex, we add purified mammalian p23, preadsorbed with the JJ3 antibody to protein A-Sepharose, to wheat geim lysate and allow ATP-dependent formation of an animal p23 centre dot plant hsp90 complex. The complex is then washed and incubated with the radiolabeled immunosuppressant drug [~3H]FK506, which binds in a specific maniier to a coimmunoadsorbed plant FKBP. Binding of the plant FKBP to plant hsp90 is prevented by adding to wheat germ lysate a purified fragment containing the TPR domains of human cyclophih'n-40, Geldanamycin, a benzoquinone ansamycin that binds to animal hsp90s and prevents their chaperone activity, binds in a temperature-dependent manner to wheat hsp90 to block formation of the p23-hsp90'FKBP heterocomplex. These data show that immunophilin binding to hsp90 via TPR domains is conserved in the plant kingdom as well as in the animal kingdom and that geldanamycin will be an important tool for the study of hsp90-mediated protein chaperoning in plant cells.