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PDBsum entry 3ooc
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Transport protein
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PDB id
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3ooc
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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 the membrane fusion protein cusb from escherichia coli.
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Authors
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C.C.Su,
F.Yang,
F.Long,
D.Reyon,
M.D.Routh,
D.W.Kuo,
A.K.Mokhtari,
J.D.Van ornam,
K.L.Rabe,
J.A.Hoy,
Y.J.Lee,
K.R.Rajashankar,
E.W.Yu.
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Ref.
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J Mol Biol, 2009,
393,
342-355.
[DOI no: ]
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PubMed id
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Abstract
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Gram-negative bacteria, such as Escherichia coli, frequently utilize tripartite
efflux complexes belonging to the resistance-nodulation-division family to expel
diverse toxic compounds from the cell. These systems contain a periplasmic
membrane fusion protein (MFP) that is critical for substrate transport. We here
present the x-ray structures of the CusB MFP from the copper/silver efflux
system of E. coli. This is the first structure of any MFPs associated with
heavy-metal efflux transporters. CusB bridges the inner-membrane efflux pump
CusA and outer-membrane channel CusC to mediate resistance to Cu(+) and Ag(+)
ions. Two distinct structures of the elongated molecules of CusB were found in
the asymmetric unit of a single crystal, which suggests the flexible nature of
this protein. Each protomer of CusB can be divided into four different domains,
whereby the first three domains are mostly beta-strands and the last domain
adopts an entirely helical architecture. Unlike other known structures of MFPs,
the alpha-helical domain of CusB is folded into a three-helix bundle. This
three-helix bundle presumably interacts with the periplasmic domain of CusC. The
N- and C-termini of CusB form the first beta-strand domain, which is found to
interact with the periplasmic domain of the CusA efflux pump. Atomic details of
how this efflux protein binds Cu(+) and Ag(+) were revealed by the crystals of
the CusB-Cu(I) and CusB-Ag(I) complexes. The structures indicate that CusB
consists of multiple binding sites for these metal ions. These findings reveal
novel structural features of an MFP in the resistance-nodulation-division efflux
system and provide direct evidence that this protein specifically interacts with
transported substrates.
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Figure 3.
Fig. 3. Structural comparison of the MFPs. (a)
Superimposition of the crystal structures of CusB (orange) and
MexA (purple). (b) Superimposition of Domain 1 of CusB (orange)
with the membrane-proximal domain of MexA (purple). (c)
Superimposition of Domain 2 of CusB (orange) with the β-barrel
domain of MexA (purple). (d) Superimposition of Domain 3 of CusB
(orange) with the lipoyl domain of MexA (purple).
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Figure 5.
Fig. 5. Cu^+- and Ag^+-binding sites of molecule A of CusB.
Cu^+ and Ag^+ ions are represented by purple and green spheres,
respectively. The overall locations of sites C1, C2, and A1 are
circled. Anomalous difference Fourier maps are contoured at 4.6
σ, 4.0 σ, and 4.2 σ for sites C1, C2, and A1, respectively.
Anomalous peak heights for sites C1′, C2′, and A1′ in
molecule B of CusB (not shown) were found to be 4.6 σ, 4.6 σ,
and 5.4 σ, respectively.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2009,
393,
342-355)
copyright 2009.
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