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PDBsum entry 2q2c
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Transport protein
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PDB id
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2q2c
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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 structures and mutational analysis of the arginine-, Lysine-, Histidine-Binding protein artj from geobacillus stearothermophilus. Implications for interactions of artj with its cognate ATP-Binding cassette transporter, Art(mp)2.
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Authors
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A.Vahedi-Faridi,
V.Eckey,
F.Scheffel,
C.Alings,
H.Landmesser,
E.Schneider,
W.Saenger.
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Ref.
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J Mol Biol, 2008,
375,
448-459.
[DOI no: ]
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PubMed id
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Abstract
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ArtJ is the substrate-binding component (receptor) of the ATP-binding cassette
(ABC) transport system ArtJ-(MP)(2) from the thermophilic bacterium Geobacillus
stearothermophilus that is specific for arginine, lysine, and histidine. The
highest affinity is found for arginine (K(d)=0.039(+/-0.014) microM), while the
affinities for lysine and histidine are about tenfold lower. We have determined
the X-ray structures of ArtJ liganded with each of these substrates at
resolutions of 1.79 A (arginine), 1.79 A (lysine), and 2.35 A (histidine),
respectively. As found for other solute receptors, the polypeptide chain is
folded into two distinct domains (lobes) connected by a hinge. The interface
between the lobes forms the substrate-binding pocket whose geometry is well
preserved in all three ArtJ/amino acid complexes. Structure-derived mutational
analyses indicated the crucial role of a region in the carboxy-terminal lobe of
ArtJ in contacting the transport pore Art(MP)(2) and revealed the functional
importance of Gln132 and Trp68. While variant Gln132Leu exhibited lower binding
affinity for arginine but no binding of lysine and histidine, the variant
Trp68Leu had lost binding activity for all three substrates. The results are
discussed in comparison with known structures of homologous proteins from
mesophilic bacteria.
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Figure 4.
Figure 4. Detailed view of the ArtJ-Arg binding pocket. (a)
Polar and hydrophobic interaction sites between the arginine
ligand and lobe I are indicated, Phe31 of the hydrophobic
sandwich Phe31/Trp68 is not shown. (b) Polar interactions
between the arginine ligand and lobe II, rotated with respect to
(a). (c) Electrostatic surface representation (red, negative;
blue, positive; yellow, neutral) of the cage-like structure of
the binding pocket, Arg is indicated by a wire model. The
direction of view is approximately along the arginine side-chain.
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Figure 6.
Figure 6. Comparison of the ArtJ-His (grey) and HisJ (green)
binding pockets. (a) Only differing residues are shown:
HisJ-Thr195 → ArtJ-Tyr205, HisJ-Leu117 → ArtJ-Gln132,
HisJ-Gln122 → ArtJ-H[2]O and ArtJ-Glu203 → HisJ-H[2]O,
ArtJ-Asp28 → HisJ-Asp11. Gln132 O^ε of ArtJ provides a
hydrogen bond to histidine that is not present in HisJ. (b)
Hydrophobic sandwich formed by the side-chain of bound histidine
and type conserved Trp68/Phe31 and Leu2/Tyr14, respectively.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2008,
375,
448-459)
copyright 2008.
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