Figure 6.
Figure 6 Model for the functional cycle of VPS4 proteins. Left:
At steady state, hVPS4B is primarily a monomeric cytoplasmic
protein (Fujita et al, 2004), and exhibits a monomer-dimer
equilibrium in the absence of bound nucleotide (Babst et al,
1998; Supplementary Figure S3). LIP5/Vta1p is an oligomer of
uncertain stoichiometry. Middle: Vps4 proteins are recruited to
sites of vesicle formation at the endosomal membrane by
interactions between the N-terminal MIT domain and the
C-proximal domains of assembled ESCRT-III lattice/cage (Babst et
al, 2002; Lin et al, 2005; Scott et al, 2005). The assembled
Vps4 proteins can also bind ATP and LIP5/Vta1p oligomers via
domain
interactions to form an enzymatically active complex. Note that
a head-to-tail orientation of the two Vps4 rings (not shown) is
equally consistent with our data. Right: We propose that bound
ESCRT-III subunits are freed from the assembled lattice/cage and
released into the cytoplasm as they are pulled up into the
narrow central chamber of the hVPS4B ring.
The above figure is reprinted
by permission from Macmillan Publishers Ltd:
EMBO J
(2005,
24,
3658-3669)
copyright 2005.
domain
interactions to form an enzymatically active complex. Note that
a head-to-tail orientation of the two Vps4 rings (not shown) is
equally consistent with our data. Right: We propose that bound
ESCRT-III subunits are freed from the assembled lattice/cage and
released into the cytoplasm as they are pulled up into the
narrow central chamber of the hVPS4B ring.