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PDBsum entry 3bzo
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Membrane protein, protein transport
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PDB id
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3bzo
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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 analysis of the essential self-Cleaving type III secretion proteins escu and spas.
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Authors
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R.Zarivach,
W.Deng,
M.Vuckovic,
H.B.Felise,
H.V.Nguyen,
S.I.Miller,
B.B.Finlay,
N.C.Strynadka.
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Ref.
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Nature, 2008,
453,
124-127.
[DOI no: ]
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PubMed id
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Abstract
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During infection by Gram-negative pathogenic bacteria, the type III secretion
system (T3SS) is assembled to allow for the direct transmission of bacterial
virulence effectors into the host cell. The T3SS system is characterized by a
series of prominent multi-component rings in the inner and outer bacterial
membranes, as well as a translocation pore in the host cell membrane. These are
all connected by a series of polymerized tubes that act as the direct conduit
for the T3SS proteins to pass through to the host cell. During assembly of the
T3SS, as well as the evolutionarily related flagellar apparatus, a
post-translational cleavage event within the inner membrane proteins EscU/FlhB
is required to promote a secretion-competent state. These proteins have long
been proposed to act as a part of a molecular switch, which would regulate the
appropriate chronological secretion of the various T3SS apparatus components
during assembly and subsequently the transported virulence effectors. Here we
show that a surface type II beta-turn in the Escherichia coli protein EscU
undergoes auto-cleavage by a mechanism involving cyclization of a strictly
conserved asparagine residue. Structural and in vivo analysis of point and
deletion mutations illustrates the subtle conformational effects of
auto-cleavage in modulating the molecular features of a highly conserved surface
region of EscU, a potential point of interaction with other T3SS components at
the inner membrane. In addition, this work provides new structural insight into
the distinct conformational requirements for a large class of self-cleaving
reactions involving asparagine cyclization.
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Figure 1.
Figure 1: Structure of the C-terminal domains of EscU and SpaS.
a, The native cleaved CTD of EscU and SpaS with a blue arrow
pointing to the auto-cleavage site. CTD is a novel  /
 -fold
with a mixed parallel and anti-parallel five-stranded twisted
-sheet
(topology 4,
1,
2,
3,
5)
flanked by two helices on each side ( 1,
2,
3
and 4).
b, Superposition of the CTD reveals a different fold for the
N-terminal linker between EscU, EscU mutants and SpaS, as well
as a longer C-terminal helix for SpaS.
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Figure 3.
Figure 3: Auto-cleaving mechanism of EscU. a, Non-cleaved
type I -bend
of P263A (left), the non-cleaved type II beta bend of N262A
(middle left), the non-cleaved type II beta bend of N262Di
(middle right) and the native cleaved loop with a flipped His
265 (right). Note the identical conformations of the N, C, C
and
C at
position 262 in all uncleaved forms. All maps are sigma-A
weighted 2F[o] - F[c] electron density (1.5  );
water molecules are represented by the red spheres. b, Detailed
mechanism for the asparagine cyclization in EscU.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2008,
453,
124-127)
copyright 2008.
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