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PDBsum entry 6a8s
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Transport protein
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PDB id
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6a8s
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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 of a putative periplasmic cystine-Binding protein from candidatus liberibacter asiaticus: insights into an adapted mechanism of ligand binding.
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Authors
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P.Kumar,
P.Kesari,
S.Kokane,
D.K.Ghosh,
P.Kumar,
A.K.Sharma.
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Ref.
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FEBS J, 2019,
286,
3450-3472.
[DOI no: ]
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PubMed id
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Abstract
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The amino acid-binding receptors, a component of ABC transporters, have evolved
to cater to different specificities and functions. Of particular interest are
cystine-binding receptors, which have shown broad specificity. In the present
study, a putative periplasmic cystine-binding protein from Candidatus
Liberibacter asiaticus (CLasTcyA) was characterized. Analysis of the CLasTcyA
sequence and crystal structures in the ligand-bound state revealed novel
features of CLasTcyA in comparison to related proteins. One of the unique
features found in CLasTcyA structure was the positioning of the C-terminal
extended loop of one chain very close to the substrate-binding site of the
adjacent monomer in the asymmetric unit. The presence of a disulphide bond,
unique to Candidatus Liberibacter family, holds the C-terminal extended loop in
position. Analysis of the substrate-binding pocket of CLasTcyA suggested a broad
specificity and a completely different orientation of the bound substrates in
comparison to related protein structures. The open conformation for one of the
two chains of the asymmetric unit in the Arg-bound structure revealed a limited
open state (18.4°) for CLasTcyA as compared to open state of other related
proteins (~ 60°). The strong interaction between Asp126 on helix-α5 of small
domain and Arg82 (bigger domain) restricts the degree of opening in ligand-free
open state. The dissociation constant of 1.26 μm by SPR and 3.7 μm by MST
exhibited low affinity for the cystine. This is the first structural
characterization of an l-cystine ABC transporter from plant pathogen and our
results suggest that CLasTcyA may have evolved to cater to its specific needs
for its survival in the host.
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