P50(CDC37) BINDS DIRECTLY TO THE CATALYTIC DOMAIN OF RAF AS WELL AS TO A SITE ON HSP90 THAT IS TOPOLOGICALLY ADJACENT TO THE TETRATRICOPEPTIDE REPEAT BINDING-SITE
Am. Silverstein et al., P50(CDC37) BINDS DIRECTLY TO THE CATALYTIC DOMAIN OF RAF AS WELL AS TO A SITE ON HSP90 THAT IS TOPOLOGICALLY ADJACENT TO THE TETRATRICOPEPTIDE REPEAT BINDING-SITE, The Journal of biological chemistry, 273(32), 1998, pp. 20090-20095
Several protein kinases (e.g. pp60(src), v-Raf) exist in heterocomplex
es with hsp90 and a 50-kDa protein that is the mammalian homolog of th
e yeast cell cycle control protein Cdc37. In contrast, unliganded ster
oid receptors exist in heterocomplexes with hsp90 and a tetratri-copep
tide repeat (TPR) domain protein, such as an immunophilin. Although p5
0(cdc37) and TPR domain proteins bind directly to hsp90, p50(cdc37) is
, not present in native steroid receptor.hsp90 heterocomplexes. To obt
ain some insight as to how v-Raf selects predominantly hsp90.p50(cdc37
) heterocomplexes, rather than hsp90 TPR protein heterocomplexes, we h
ave examined the binding of p50(cdc37) to hsp90 and to Raf. We show th
at p50(cdc37) exists in separate hsp90 heterocomplexes from the TPR do
main proteins and that intact TPR proteins compete for p50(cdc37) bind
ing to hsp90 but a protein fragment containing a TPR domain does not.
This suggests that the binding site for p50(cdc37) Lies topologically
adjacent to the TPR acceptor site on the surface of hsp90. Also, we sh
ow that p50(cdc37) binds directly to v-Raf, with the catalytic domain
of Raf being sufficient. We propose that the combination of exclusive
binding of p50(cdc37) versus a TPR domain protein to hsp90 plus direct
binding of p50(cdc37) to Raf allows the protein kinase to select for
the dominant hsp90 p50(cdc37) composition that is observed with a vari
ety of protein kinase heterocomplexes immunoadsorbed from cytosols.