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PDBsum entry 4xtc
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Transport protein
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PDB id
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4xtc
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Contents |
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288 a.a.
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287 a.a.
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363 a.a.
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492 a.a.
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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 solute-Binding protein in the closed conformation induces ATP hydrolysis in a bacterial ATP-Binding cassette transporter involved in the import of alginate.
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Authors
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A.Kaneko,
K.Uenishi,
Y.Maruyama,
N.Mizuno,
S.Baba,
T.Kumasaka,
B.Mikami,
K.Murata,
W.Hashimoto.
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Ref.
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J Biol Chem, 2017,
292,
15681-15690.
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PubMed id
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Abstract
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The Gram-negative bacteriumSphingomonassp. A1 incorporates alginate into
cells via the cell-surface pit without prior depolymerization by extracellular
enzymes. Alginate import across cytoplasmic membranes thereby depends on the
ATP-binding cassette transporter AlgM1M2SS (a heterotetramer of AlgM1, AlgM2,
and AlgS), which cooperates with the periplasmic solute-binding protein AlgQ1 or
AlgQ2; however, several details of AlgM1M2SS-mediated alginate import are not
well-understood. Herein, we analyzed ATPase and transport activities of
AlgM1M2SS after reconstitution into liposomes with AlgQ2 and alginate
oligosaccharide substrates having different polymerization degrees (PDs). Longer
alginate oligosaccharides (PD ≥ 5) stimulated the ATPase activity of AlgM1M2SS
but were inert as substrates of AlgM1M2SS-mediated transport, indicating that
AlgM1M2SS-mediated ATP hydrolysis can be stimulated independently of substrate
transport. Using X-ray crystallography in the presence of AlgQ2 and long
alginate oligosaccharides (PD 6-8) and with the humid air and glue-coating
method, we determined the crystal structure of AlgM1M2SS in complex with
oligosaccharide-bound AlgQ2 at 3.6 Å resolution. The structure of the
ATP-binding cassette transporter in complex with non-transport ligand-bound
periplasmic solute-binding protein revealed that AlgM1M2SS and AlgQ2 adopt
inward-facing and closed conformations, respectively. Thesein vitroassays
and structural analyses indicated that interactions between AlgM1M2SS in the
inward-facing conformation and periplasmic ligand-bound AlgQ2 in the closed
conformation induce ATP hydrolysis by the ATP-binding protein AlgS. We conclude
that substrate-bound AlgQ2 in the closed conformation initially interacts with
AlgM1M2SS, the AlgM1M2SS-AlgQ2 complex then forms, and this formation is
followed by ATP hydrolysis.
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