FOLDING OF THE GLUCOCORTICOID RECEPTOR BY THE HEAT-SHOCK-PROTEIN (HSP) 90-BASED CHAPERONE MACHINERY - THE ROLE OF P23 IS TO STABILIZE RECEPTOR-HSP90 HETEROCOMPLEXES FORMED BY HSP90-P60-HSP70
Kd. Dittmar et al., FOLDING OF THE GLUCOCORTICOID RECEPTOR BY THE HEAT-SHOCK-PROTEIN (HSP) 90-BASED CHAPERONE MACHINERY - THE ROLE OF P23 IS TO STABILIZE RECEPTOR-HSP90 HETEROCOMPLEXES FORMED BY HSP90-P60-HSP70, The Journal of biological chemistry, 272(34), 1997, pp. 21213-21220
In cytosols from animal and plant cells, the abundant heat shock prote
in hsp90 is associated with several proteins that act together to asse
mble steroid receptors into receptor-hsp90 heterocomplexes. We have re
constituted a minimal receptor hsp90 assembly system containing four r
equired components, hsp90, hsp70, p60, and p23 (Dittmar, K, D,, Hutchi
son, K, A., Owens-Grille, J, IG,, and Pratt, W, B, (1996) J, Biol. Che
m, 271, 12833-12839), We have shown that hsp90, p60, and hsp70 are suf
ficient for carrying out the folding change that converts the glucocor
ticoid receptor (GR) hormone binding domain (HBD) from a non-steroid b
inding to a steroid binding conformation, but to form stable GR hsp90
heterocomplexes, p23 must also be present in the incubation mix (Dittm
ar, K, D,, and Pratt, W, B. (1997) J, Biol, Chem. 272, 13047-13054), I
n this work, we show that addition of p23 to native GR.hsp90 heterocom
plexes immunoadsorbed from L cell cytosol or to GR.hsp90 heterocomplex
es prepared with the minimal (hsp90.p60.hsp70) assembly system inhibit
s both receptor heterocomplex disassembly and loss of steroid binding
activity, p23 stabilizes the GR.hsp90 heterocomplex in a dynamic and A
TP-independent manner. In contrast to hsp90 that is bound to the GR, f
ree hsp90 binds p23 in an ATP-dependent manner, and hsp90 in the hsp90
p60 hsp70 heterocomplex is in a conformation that does not bind p23 a
t all, The effect of p23 in the minimal GR heterocomplex assembly syst
em is to stabilize GR.hsp90 heterocomplexes once they are formed and i
t does not appear to affect the rate of heterocomplex assembly, Molybd
ate has the same ability as p23 to stabilize GR heterocomplexes with m
ammalian hsp90, but GR heterocomplexes with plant hsp90 are stabilized
by p23 and not by molybdate, We propose that incubation of the GR.wit
h hsp90 p60]hsp70 forms a GR hsp90 heterocomplex in which hsp90 is in
an ATP-dependent conformation, The ATP dependent conformation of hsp90
is required for the hormone binding domain to have a steroid binding
site, and binding of p23 to that state of hsp90 stabilizes the GR.hsp9
0 heterocomplex to inactivation and disassembly.