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PDBsum entry 4bbk
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Cell adhesion
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PDB id
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4bbk
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References listed in PDB file
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Key reference
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Title
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Structural and functional characterization of the kindlin-1 pleckstrin homology domain.
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Authors
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L.A.Yates,
C.N.Lumb,
N.N.Brahme,
R.Zalyte,
L.E.Bird,
L.De colibus,
R.J.Owens,
D.A.Calderwood,
M.S.Sansom,
R.J.Gilbert.
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Ref.
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J Biol Chem, 2012,
287,
43246-43261.
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PubMed id
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Abstract
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Inside-out activation of integrins is mediated via the binding of talin and
kindlin to integrin β-subunit cytoplasmic tails. The kindlin FERM domain is
interrupted by a pleckstrin homology (PH) domain within its F2 subdomain. Here,
we present data confirming the importance of the kindlin-1 PH domain for
integrin activation and its x-ray crystal structure at a resolution of 2.1 Å
revealing a C-terminal second α-helix integral to the domain but found only in
the kindlin protein family. An isoform-specific salt bridge occludes the
canonical phosphoinositide binding site, but molecular dynamics simulations
display transient switching to an alternative open conformer. Molecular docking
reveals that the opening of the pocket would enable potential ligands to bind
within it. Although lipid overlay assays suggested the PH domain binds inositol
monophosphates, surface plasmon resonance demonstrated weak affinities for
inositol 3,4,5-triphosphate (Ins(3,4,5)P(3); K(D) ∼100 μm) and no
monophosphate binding. Removing the salt bridge by site-directed mutagenesis
increases the PH domain affinity for Ins(3,4,5)P(3) as measured by surface
plasmon resonance and enables it to bind PtdIns(3,5)P(2) on a dot-blot.
Structural comparison with other PH domains suggests that the phosphate binding
pocket in the kindlin-1 PH domain is more occluded than in kindlins-2 and -3 due
to its salt bridge. In addition, the apparent affinity for Ins(3,4,5)P(3) is
affected by the presence of PO(4) ions in the buffer. We suggest the
physiological ligand of the kindlin-1 PH domain is most likely not an inositol
phosphate but another phosphorylated species.
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