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PDBsum entry 3jrm
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Hydrolase/hydrolase activator
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PDB id
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3jrm
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Contents |
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(+ 1 more)
227 a.a.
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(+ 1 more)
203 a.a.
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(+ 1 more)
218 a.a.
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References listed in PDB file
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Key reference
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Title
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Structural models for interactions between the 20s proteasome and its pan/19s activators.
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Authors
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B.M.Stadtmueller,
K.Ferrell,
F.G.Whitby,
A.Heroux,
H.Robinson,
D.G.Myszka,
C.P.Hill.
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Ref.
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J Biol Chem, 2010,
285,
13-17.
[DOI no: ]
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PubMed id
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Abstract
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Proteasome activity is regulated by sequestration of its proteolytic centers in
a barrel-shaped structure that limits substrate access. Substrates enter the
proteasome by means of activator complexes that bind to the end rings of
proteasome alpha subunits and induce opening of an axial entrance/exit pore. The
PA26 activator binds in a pocket on the proteasome surface using main chain
contacts of its C-terminal residues and uses an internal activation loop to
trigger gate opening by repositioning the proteasome Pro-17 reverse turn.
Subunits of the unrelated PAN/19S activators bind with their C termini in the
same pockets but can induce proteasome gate opening entirely from interactions
of their C-terminal peptides, which are reported to cause gate opening by
inducing a rocking motion of proteasome alpha subunits rather than by directly
contacting the Pro-17 turn. Here we report crystal structures and binding
studies of proteasome complexes with PA26 constructs that display modified
C-terminal residues, including those corresponding to PAN. These findings
suggest that PA26 and PAN/19S C-terminal residues bind superimposably and that
both classes of activator induce gate opening by using direct contacts to
residues of the proteasome Pro-17 reverse turn. In the case of the PAN and 19S
activators, a penultimate tyrosine/phenylalanine residue contacts the proteasome
Gly-19 carbonyl oxygen to stabilize the open conformation.
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Figure 1.
Structures of PA26-proteasome complexes. A, overall structure
with one PA26 subunit colored blue and its three C-terminal
residues in space-filling representation. Proteasome subunits
that form the corresponding binding pocket are pink and gray
(white in subsequent panels). B, close-up showing main chain
hydrogen-bonding interactions of the PA26 C-terminal residues
(31). C, sequences and structures of PA26 (31) and variants
described in this work shown after overlap on the proteasome
structures. D, the penultimate Tyr-230 residue contacts Gly-19
to reposition the Pro-17 turn. Distances between Tyr-230-OH and
Gly-19-O in closed (red; modeled) and open (green; observed)
conformations are shown. Pro-17 undergoes an apparent movement
of ∼1 Å. H0, helix 0. E, binding pocket with proteasome
shown as a semitransparent molecular surface. Conserved residues
whose side chains contact the activator C-terminal residues are
indicated. F, V230F penultimate phenylalanine interactions
observed with Gly-19 in the open conformation (pink) and modeled
in the closed conformation (blue). To best describe contacts,
riding hydrogen atoms were included in determined structures and
assessed with MolProbity (36).
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Figure 2.
PA26-proteasome binding studies. A–E, biosensorgrams
showing concentration-dependent binding of PA26 variants to the
S. cerevisiae proteasome and calculated average dissociation
constants (K[D]). Binding to an IgG control surface was
negligible (data not shown). RU, response units. F, kinetic plot
of k[a] versus k[d] where diagonals represent K[D], and values
for each PA26 variant are shown as spots. The K[D] standard
deviation is less than the size of the spots.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2010,
285,
13-17)
copyright 2010.
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