TY - JOUR
T1 - Recognition of misfolding proteins by PA700, the regulatory subcomplex of the 26 S proteasome
AU - Strickland, Elizabeth
AU - Hakala, Kevin
AU - Thomas, Philip J.
AU - DeMartino, George N.
PY - 2000/2/25
Y1 - 2000/2/25
N2 - The 26 S proteasome is a large protease complex that catalyzes the degradation of both native and misfolded proteins. These proteins are known to interact with PA700, the regulatory subcomplex of the 26 S proteasome, via a covalently attached polyubiquitin chain. Here we provide evidence for an additional ubiquitin-independent mode of substrate recognition by PA700. PA700 prevents the aggregation of three incompletely folded, nonubiquitinated substrates: the ΔF-508 mutant form of cystic fibrosis transmembrane regulator, nucleotide binding domain 1, insulin B chain, and citrate synthase. This function does not require ATP hydrolysis. The stoichiometry required for this function, the effect of PA700 on the lag phase of aggregation, and the temporal specificity of PA700 in this process all indicate that PA700 interacts with a subpopulation of non-native conformations that is either particularly aggregation-prone or nucleates misassociation reactions. The inhibition of off-pathway self-association reactions is also reflected in the ability of PA700 to promote refolding of citrate synthase. These results provide evidence that, in addition to binding polyubiquitin chains, PA700 contains a site(s) that recognizes and interacts with misfolded or partially denatured polypeptides. This feature supplies an additional level of substrate specificity to the 26 S proteasome and a means by which substrates are maintained in a soluble state until refolding or degradation is complete.
AB - The 26 S proteasome is a large protease complex that catalyzes the degradation of both native and misfolded proteins. These proteins are known to interact with PA700, the regulatory subcomplex of the 26 S proteasome, via a covalently attached polyubiquitin chain. Here we provide evidence for an additional ubiquitin-independent mode of substrate recognition by PA700. PA700 prevents the aggregation of three incompletely folded, nonubiquitinated substrates: the ΔF-508 mutant form of cystic fibrosis transmembrane regulator, nucleotide binding domain 1, insulin B chain, and citrate synthase. This function does not require ATP hydrolysis. The stoichiometry required for this function, the effect of PA700 on the lag phase of aggregation, and the temporal specificity of PA700 in this process all indicate that PA700 interacts with a subpopulation of non-native conformations that is either particularly aggregation-prone or nucleates misassociation reactions. The inhibition of off-pathway self-association reactions is also reflected in the ability of PA700 to promote refolding of citrate synthase. These results provide evidence that, in addition to binding polyubiquitin chains, PA700 contains a site(s) that recognizes and interacts with misfolded or partially denatured polypeptides. This feature supplies an additional level of substrate specificity to the 26 S proteasome and a means by which substrates are maintained in a soluble state until refolding or degradation is complete.
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U2 - 10.1074/jbc.275.8.5565
DO - 10.1074/jbc.275.8.5565
M3 - Article
C2 - 10681537
AN - SCOPUS:0034090632
SN - 0021-9258
VL - 275
SP - 5565
EP - 5572
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 8
ER -