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PDBsum entry 7a5c
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Transport protein
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PDB id
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7a5c
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References listed in PDB file
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Key reference
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Title
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Triggering closure of a sialic acid trap transporter substrate binding protein through binding of natural or artificial substrates.
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Authors
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M.F.Peter,
C.Gebhardt,
J.Glaenzer,
N.Schneberger,
M.De boer,
G.H.Thomas,
T.Cordes,
G.Hagelueken.
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Ref.
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J Mol Biol, 2020,
433,
166756.
[DOI no: ]
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PubMed id
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Abstract
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The pathogens Vibrio cholerae and Haemophilus influenzae use tripartite
ATP-independent periplasmic transporters (TRAPs) to scavenge sialic acid from
host tissues. They use it as a nutrient or to evade the innate immune system by
sialylating surface lipopolysaccharides. An essential component of TRAP
transporters is a periplasmic substrate binding protein (SBP). Without
substrate, the SBP has been proposed to rest in an open-state, which is not
recognised by the transporter. Substrate binding induces a conformational change
of the SBP and it is thought that this closed state is recognised by the
transporter, triggering substrate translocation. Here we use real time single
molecule FRET experiments and crystallography to investigate the open- to
closed-state transition of VcSiaP, the SBP of the sialic acid TRAP transporter
from V. cholerae. We show that the conformational switching of VcSiaP is
strictly substrate induced, confirming an important aspect of the proposed
transport mechanism. Two new crystal structures of VcSiaP provide insights into
the closing mechanism. While the first structure contains the natural ligand,
sialic acid, the second structure contains an artificial peptide in the sialic
acid binding site. Together, the two structures suggest that the ligand itself
stabilises the closed state and that SBP closure is triggered by physically
bridging the gap between the two lobes of the SBP. Finally, we demonstrate that
the affinity for the artificial peptide substrate can be substantially increased
by varying its amino acid sequence and by this, serve as a starting point for
the development of peptide-based inhibitors of TRAP transporters.
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