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PDBsum entry 3da3
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References listed in PDB file
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Key reference
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Title
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Crystal structure of colicin m, A novel phosphatase specifically imported by escherichia coli.
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Authors
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K.Zeth,
C.Römer,
S.I.Patzer,
V.Braun.
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Ref.
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J Biol Chem, 2008,
283,
25324-25331.
[DOI no: ]
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PubMed id
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Abstract
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Colicins are cytotoxic proteins secreted by certain strains of Escherichia coli.
Colicin M is unique among these toxins in that it acts in the periplasm and
specifically inhibits murein biosynthesis by hydrolyzing the pyrophosphate
linkage between bactoprenol and the murein precursor. We crystallized colicin M
and determined the structure at 1.7A resolution using x-ray crystallography. The
protein has a novel structure composed of three domains with distinct functions.
The N-domain is a short random coil and contains the exposed TonB box. The
central domain includes a hydrophobic alpha-helix and binds presumably to the
FhuA receptor. The C-domain is composed of a mixed alpha/beta-fold and forms the
phosphatase. The architectures of the individual modules show no similarity to
known structures. Amino acid replacements in previously isolated inactive
colicin M mutants are located in the phosphatase domain, which contains a number
of surface-exposed residues conserved in predicted bacteriocins of other
bacteria. The novel phosphatase domain displays no sequence similarity to known
phosphatases. The N-terminal and central domains are not conserved among
bacteriocins, which likely reflect the distinct import proteins required for the
uptake of the various bacteriocins. The homology pattern supports our previous
proposal that colicins evolved by combination of distinct functional domains.
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Figure 3.
FIGURE 3. Similarities of colicin M to other protein
structures. A, simulated annealed 2F[o] - F[c] map of the
N-terminal TonB-box domain. B, superposition of the N termini of
colicin M (white), FhuA (magenta; in complex with a TonB
fragment; PDB entry 2GRX), and BtuB (cyan; in complex with a
TonB fragment; PDB entry 2GSK). C, superposition of the
C-terminal domain of colicin M (gray) with the membrane-spanning
part of the outer membrane transporter Hia of H. influenzae
(red, blue, and green) (39).
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Figure 5.
FIGURE 5. Tentative model of colicin M uptake across the
outer membrane (OM) of E. coli. I, colicin M (crystal structure)
binds to the FhuA protein, whose crystal structure is shown. II,
colicin M partially unfolds while bound to FhuA. III, N-terminal
domain (red) with the TonB box (yellow) enters the pore in FhuA,
which is formed by interaction of FhuA with energized TonB
(green), leading to movement of the globular domain (cork) out
of FhuA. IV, TonB box of colicin M interacts with TonB, and
colicin M unfolds further and enters the periplasm through the
FhuA pore. VI, in the periplasm, colicin M is refolded with the
help of the FkpA chaperon and cleaves the pyrophosphate bond
between C55 isoprenoid and the murein precursor. IM, inner
membrane;  , membrane potential.
For the sake of clarity, the ExbB and ExbD proteins associated
with TonB and required for TonB activity are not shown.
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The above figures are
reprinted
from an Open Access publication published by the ASBMB:
J Biol Chem
(2008,
283,
25324-25331)
copyright 2008.
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