THE ROLE OF DNAJ-LIKE PROTEINS IN GLUCOCORTICOID RECEPTOR-CENTER-DOT-HSP90 HETEROCOMPLEX ASSEMBLY BY THE RECONSTITUTED HSP90-CENTER-DOT-P60-CENTER-DOT-HSP70 FOLDOSOME COMPLEX
Kd. Dittmar et al., THE ROLE OF DNAJ-LIKE PROTEINS IN GLUCOCORTICOID RECEPTOR-CENTER-DOT-HSP90 HETEROCOMPLEX ASSEMBLY BY THE RECONSTITUTED HSP90-CENTER-DOT-P60-CENTER-DOT-HSP70 FOLDOSOME COMPLEX, The Journal of biological chemistry, 273(13), 1998, pp. 7358-7366
The glucocorticoid receptor (GR) is recovered from hormone-free cells
in a heterocomplex with the molecular chaperone hsp90, which is requir
ed to produce the proper folding state for steroid binding. GR.hsp90 h
eterocomplexes are formed by a multiprotein system that appears to exi
st in all eukaryotic cells, Recently, we have reconstituted a receptor
.hsp90 heterocomplex assembly system with purified rabbit hsp90 and hs
p70 and bacterially expressed human p23 and p60. We have shown that hs
p90, p60, and hsp70 form an hsp90.p60.hsp70 complex that converts the
GR from a non-steroid binding to a steroid binding form (Dittmar, K. D
., and Pratt, W. B. (1997) J. Biol. Chem. 272, 13047-13054). The resul
ting GR.hsp90 heterocomplex rapidly disassembles unless p23 is present
to bind to the ATP-dependent conformation of hsp90 and stabilize its
association with the receptor (Dittmar, K. D., Demady, D., R., Stancat
o, L. F., Krishna, P., and Pratt, W. B. (1997) J. Biol. Chem. 272, 212
13-21220). In the current work, we show that the purified rabbit hsp70
utilized in prior studies is contaminated with a small amount of the
rabbit DnaJ homolog hsp40. Elimination of the hsp40 from the purified
GR.hsp90 assembly system reduces assembly activity, and the activity i
s restored by addition of the purified yeast DnaJ homolog YDJ-1. hsp40
is a component of the hsp90.p60.hsp70 foldosome complex isolated from
reticulocyte lysate with antibody against p60. Under conditions that
promote binding of p23 to hsp90 (elevated temperature, ATP, Nonidet P-
40, molybdate), a five-membered (p23.hsp90.p60.hsp70.hsp40) complex of
chaperone proteins is formed in reticulocyte lysate or from purified
proteins. The hsp40-free, purified assembly system has a modest level
of assembly activity that is maximally potentiated by YDJ-1 when it is
present at about one-twentieth the concentration of hsp70. Although h
sp40 is not in the final GR.hsp90 heterocomplex isolated from L cell c
ytosol, it is in the GR.hsp90 heterocomplex assembled in reticulocyte
lysate. We conclude that hsp40 is a component of the multiprotein hsp9
0-based chaperone system where it potentiates GR.hsp90 heterocomplex a
ssembly.