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PDBsum entry 2ffb
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Transport protein
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PDB id
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2ffb
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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 structural analysis of asymmetry required for catalytic activity of an abc-Atpase domain dimer.
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Authors
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J.Zaitseva,
C.Oswald,
T.Jumpertz,
S.Jenewein,
A.Wiedenmann,
I.B.Holland,
L.Schmitt.
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Ref.
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EMBO J, 2006,
25,
3432-3443.
[DOI no: ]
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PubMed id
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Abstract
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The ATP-binding cassette (ABC)-transporter haemolysin (Hly)B, a central element
of a Type I secretion machinery, acts in concert with two additional proteins in
Escherichia coli to translocate the toxin HlyA directly from the cytoplasm to
the exterior. The basic set of crystal structures necessary to describe the
catalytic cycle of the isolated HlyB-NBD (nucleotide-binding domain) has now
been completed. This allowed a detailed analysis with respect to hinge regions,
functionally important key residues and potential energy storage devices that
revealed many novel features. These include a structural asymmetry within the
ATP dimer that was significantly enhanced in the presence of Mg2+, indicating a
possible functional asymmetry in the form of one open and one closed phosphate
exit tunnel. Guided by the structural analysis, we identified two amino acids,
closing one tunnel by an apparent salt bridge. Mutation of these residues
abolished ATP-dependent cooperativity of the NBDs. The implications of these new
findings for the coupling of ATP binding and hydrolysis to functional activity
are discussed.
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Figure 1.
Figure 1 The catalytic cycle of the HlyB-NBD. Crystal structures
of the monomeric nucleotide-free (Schmitt et al, 2003), dimeric
ATP-bound (H662A and E631Q) and monomeric ADP-bound (wild type,
E631Q and H662A) forms (this study) are shown. For simplicity,
the structure of the ATP/Mg^2+-bound form (Zaitseva et al,
2005a) is not shown. The catalytic domain is colored in light
yellow and the helical domain in light tan. Conserved motifs are
highlighted and color-coded as follows: Walker A (residues
502–510, blue), Q-loop (residues 549–556, brown),
ABC-signature motif (residues 606–610, red), Pro-loop
(residues 623–625, orange), Walker B (residues 626–630,
magenta), D-loop (residues 634–637, black) and H-loop
(residues 661–663, green). Bound ligands are shown in
ball-and-stick representation. K[D] values were taken from
Zaitseva et al (2005b).
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Figure 2.
Figure 2 Nucleotide-binding sites. Stereoview of the ATP-binding
(A) and ATP/Mg^2+-binding(B) sites. Color-coding is identical to
Figure 1. Direct and water-mediated protein–ATP interactions
are highlighted in yellow. Water molecules are shown as blue
spheres and Mg^2+ as a green sphere. The interaction between
D637 of the D-loop of the trans monomer and S504 of the Walker A
motif of the cis monomer is indicated. ATP and amino acids
involved in ligand interactions are shown in ball-and-stick
representation. ^* indicates conserved motifs of the trans
monomer participating in ATP coordination. (C) Stereoview of the
ADP-binding site. ADP and residues involved in ligand
interactions are shown in ball-and-stick representation, water
molecules are blue spheres, protein–ADP interactions are
highlighted in green and ADP–water interactions in blue.
Color-coding is identical to Figure 1. The interaction between
the side chain of Q550 and the amide backbone of T633 is
highlighted by a dashed, brown line.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
EMBO J
(2006,
25,
3432-3443)
copyright 2006.
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