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PDBsum entry 2fn9
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Sugar binding protein
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PDB id
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2fn9
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References listed in PDB file
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Key reference
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Title
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Ligand-Induced conformational changes in a thermophilic ribose-Binding protein.
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Authors
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M.J.Cuneo,
L.S.Beese,
H.W.Hellinga.
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Ref.
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Bmc Struct Biol, 2008,
8,
50-50.
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PubMed id
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Abstract
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BACKGROUND: Members of the periplasmic binding protein (PBP) superfamily are
involved in transport and signaling processes in both prokaryotes and
eukaryotes. Biological responses are typically mediated by ligand-induced
conformational changes in which the binding event is coupled to a hinge-bending
motion that brings together two domains in a closed form. In all PBP-mediated
biological processes, downstream partners recognize the closed form of the
protein. This motion has also been exploited in protein engineering experiments
to construct biosensors that transduce ligand binding to a variety of physical
signals. Understanding the mechanistic details of PBP conformational changes,
both global (hinge bending, twisting, shear movements) and local (rotamer
changes, backbone motion), therefore is not only important for understanding
their biological function but also for protein engineering experiments. RESULTS:
Here we present biochemical characterization and crystal structure determination
of the periplasmic ribose-binding protein (RBP) from the hyperthermophile
Thermotoga maritima in its ribose-bound and unliganded state. The T. maritima
RBP (tmRBP) has 39% sequence identity and is considerably more resistant to
thermal denaturation (app Tm value is 108 degrees C) than the mesophilic
Escherichia coli homolog (ecRBP) (app Tm value is 56 degrees C). Polar ligand
interactions and ligand-induced global conformational changes are conserved
among ecRBP and tmRBP; however local structural rearrangements involving
side-chain motions in the ligand-binding site are not conserved. CONCLUSION:
Although the large-scale ligand-induced changes are mediated through similar
regions, and are produced by similar backbone movements in tmRBP and ecRBP, the
small-scale ligand-induced structural rearrangements differentiate the mesophile
and thermophile. This suggests there are mechanistic differences in the manner
by which these two proteins bind their ligands and are an example of how two
structurally similar proteins utilize different mechanisms to form a
ligand-bound state.
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