Xh. Lu et al., Heat shock protein-90 and the catalytic activities of the 20 S proteasome (multicatalytic proteinase complex), ARCH BIOCH, 387(1), 2001, pp. 163-171
The effect of heat shock protein 90 (Hsp-90) and several other proteins on
the catalytic activities of the 20 S proteasome (MPC) was examined. The chy
motrypsin-like (ChT-L) and peptidylglutamyl-peptide hydrolyzing (PGPH) acti
vities of the pituitary MPC were inhibited by Hsp-90 with IC50 values of 8
and 28 nM, respectively. Bovine serum albumin and two other proteins tested
inhibited the same activities with much higher IC50 values. The trypsin-li
ke and branched-chain amino-acid-preferring activities were not affected by
any of the proteins, None of the activities of the bovine spleen MPC, an e
nzyme form in which the X, Y, and Z subunits are virtually completely repla
ced by the LMP2, LMP7, and LMP10 subunits, was affected by either Hsp-90 or
the other proteins tested. Hsp-90 inhibited the degradation of the oxidize
d B-chain of insulin by the pituitary MPC hut not by its spleen counterpart
. The PA28 activator (11 S regulator; REG) of the proteasome abolished the
inhibitory effect of Hsp-90 and other proteins on the ChT-L and PGPH activi
ties of the pituitary MPC. It is suggested that Hsp-90 induces conformation
al changes that affect the ChT-L and PGPH activities expressed by the X and
Y subunits, respectively, but does not affect the activities expressed by
LMP subunits. (C) 2001 Academic Press.