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PDBsum entry 2zcy
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Contents |
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250 a.a.
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244 a.a.
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241 a.a.
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242 a.a.
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233 a.a.
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244 a.a.
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243 a.a.
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222 a.a.
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204 a.a.
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198 a.a.
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212 a.a.
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222 a.a.
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233 a.a.
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196 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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A plant pathogen virulence factor inhibits the eukaryotic proteasome by a novel mechanism.
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Authors
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M.Groll,
B.Schellenberg,
A.S.Bachmann,
C.R.Archer,
R.Huber,
T.K.Powell,
S.Lindow,
M.Kaiser,
R.Dudler.
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Ref.
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Nature, 2008,
452,
755-758.
[DOI no: ]
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PubMed id
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Abstract
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Pathogenic bacteria often use effector molecules to increase virulence. In most
cases, the mode of action of effectors remains unknown. Strains of Pseudomonas
syringae pv. syringae (Pss) secrete syringolin A (SylA), a product of a mixed
non-ribosomal peptide/polyketide synthetase, in planta. Here we identify SylA as
a virulence factor because a SylA-negative mutant in Pss strain B728a obtained
by gene disruption was markedly less virulent on its host, Phaseolus vulgaris
(bean). We show that SylA irreversibly inhibits all three catalytic activities
of eukaryotic proteasomes, thus adding proteasome inhibition to the repertoire
of modes of action of virulence factors. The crystal structure of the yeast
proteasome in complex with SylA revealed a novel mechanism of covalent binding
to the catalytic subunits. Thus, SylA defines a new class of proteasome
inhibitors that includes glidobactin A (GlbA), a structurally related compound
from an unknown species of the order Burkholderiales, for which we demonstrate a
similar proteasome inhibition mechanism. As proteasome inhibitors are a
promising class of anti-tumour agents, the discovery of a novel family of
inhibitory natural products, which we refer to as syrbactins, may also have
implications for the development of anti-cancer drugs. Homologues of SylA and
GlbA synthetase genes are found in some other pathogenic bacteria, including the
human pathogen Burkholderia pseudomallei, the causative agent of melioidosis. It
is thus possible that these bacteria are capable of producing proteasome
inhibitors of the syrbactin class.
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Figure 1.
Figure 1: Syringolin-negative mutant exhibits reduced virulence.
Five pots per experiment (Exp), each with eight 18-day-old
bean plants, were spray-inoculated with 10^5 cells per
millilitre of wild-type or SylA-negative (sylC KO) strains of
Pss B728a. Lesion numbers per trifoliate leaf were counted on
the oldest (O) and middle-aged (M) leaves. Mean lesion numbers
s.d. over the five replica pots are given. p, error probability
(two-sided t-test).
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Figure 3.
Figure 3: Structural basis for proteasome inhibition by
syrbactins. a, Chemical structure of SylA and GlbA. Red,  ,
 -unsaturated
carbonyl group reacting with Thr1O^  ;
green, dipeptide bond stabilizing the inhibitor upon proteasome
binding; blue, molecule part determining active site
specificity; yellow, aliphatic tail of GlbA. b, Mechanism of
binding of SylA/GlbA to the active site Thr1. c, d, Stereo
representation of the chymotryptic-like active site (rose,
subunit 5;
light blue, subunit 6)
in complex with (c) SylA (green; PDB accession code ) and (d)
GlbA (green, aliphatic tail in yellow; PDB accession code ).
Magenta, covalent linkage of inhibitors with active site Thr1;
dotted lines indicate hydrogen bonds. Black, residues performing
specific interactions with SylA and GlbA. Electron-density maps
(grey) are contoured from 1  in
similar orientations around Thr1. e, Electrostatic potential
surface (contoured from +15kT/e (intense blue) to -15kT/e
(intense red)) of SylA bound to subunit 5.
f, Structural superposition of SylA (green) with GlbA (yellow)
bound to subunit 5.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2008,
452,
755-758)
copyright 2008.
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