Ye, Yihong; Meyer, Hemmo; Rapoport, Tom A.:

Function of the p97–Ufd1–Npl4 complex in retrotranslocation from the ER to the cytosol: dual recognition of nonubiquitinated polypeptide segments and polyubiquitin chains

In: The journal of cell biology : JCB, Jg. 162 (2003) ; Nr. 1, S. 71-84
ISSN: 0021-9525
Zeitschriftenaufsatz / Fach: Biologie
member of the family of ATPases associated with
diverse cellular activities, called p97 in mammals
and Cdc48 in yeast, associates with the cofactor
Ufd1–Npl4 to move polyubiquitinated polypeptides from
the endoplasmic reticulum (ER) membrane into the cytosol
for their subsequent degradation by the proteasome. Here, we
have studied the mechanism by which the p97–Ufd1–Npl4
complex functions in this retrotranslocation pathway.
Substrate binding occurs when the first ATPase domain of
p97 (D1 domain) is in its nucleotide-bound state, an interaction
that also requires an association of p97 with the
membrane through its NH
-terminal domain. The two ATPase
domains (D1 and D2) of p97 appear to alternate in ATP
hydrolysis, which is essential for the movement of polypeptides
from the ER membrane into the cytosol. The ATPase
itself can interact with nonmodified polypeptide substrates
as they emerge from the ER membrane. Polyubiquitin chains
linked by lysine 48 are recognized in a synergistic manner
by both p97 and an evolutionarily conserved ubiquitinbinding
site at the NH
terminus of Ufd1. We propose a
dual recognition model in which the ATPase complex
binds both a nonmodified segment of the substrate and the
attached polyubiquitin chain; polyubiquitin binding may
activate the ATPase p97 to pull the polypeptide substrate
out of the membrane.