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PDBsum entry 2v6v
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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 membrane binding analysis of the phox homology domain of bem1p: basis of phosphatidylinositol 4-Phosphate specificity.
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Authors
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R.V.Stahelin,
D.Karathanassis,
D.Murray,
R.L.Williams,
W.Cho.
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Ref.
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J Biol Chem, 2007,
282,
25737-25747.
[DOI no: ]
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PubMed id
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Note: In the PDB file this reference is
annotated as "TO BE PUBLISHED". The citation details given above have
been manually determined.
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Abstract
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Phox homology (PX) domains, which have been identified in a variety of proteins
involved in cell signaling and membrane trafficking, have been shown to interact
with phosphoinositides (PIs) with different affinities and specificities. To
elucidate the structural origin of the diverse PI specificity of PX domains, we
determined the crystal structure of the PX domain from Bem1p that has been
reported to bind phosphatidylinositol 4-phosphate (PtdIns(4)P). We also measured
the membrane binding properties of the PX domain and its mutants by surface
plasmon resonance and monolayer techniques and calculated the electrostatic
potentials for the PX domain in the absence and presence of bound PtdIns(4)P.
The Bem1p PX domain contains a signature PI-binding site optimized for
PtdIns(4)P binding and also harbors basic and hydrophobic residues on the
membrane-binding surface. The membrane binding of the Bem1p PX domain is
initiated by nonspecific electrostatic interactions between the cationic
membrane-binding surface of the domain and anionic membrane surfaces, followed
by the membrane penetration of hydrophobic residues. Unlike other PX domains,
the Bem1p PX domain has high intrinsic membrane penetrating activity in the
absence of PtdIns(4)P, suggesting that the partial membrane penetration may
occur before specific PtdIns(4)P binding and last after the removal of
PtdIns(4)P under certain conditions. This structural and functional study of the
PtdIns(4)P-binding Bem1p PX domain provides new insight into the diverse PI
specificities and membrane-binding mechanisms of PX domains.
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Figure 4.
Monolayer penetration of the Bem1p PX and OSBP and FAPP1 PH
domains into various phospholipids.A, Δπ was measured as a
function of π[0] for wild-type Bem1p-PX with POPC/POPE (80:20)
(○), POPC/POPE/PtdIns(4)P (77:20:3) (•),
POPC/POPE/PtdIns(3)P (77:20:3) (▪), POPC/POPE/PtdIns(5)P
(77:20:3) (▴), and POPC/POPE/POPS (60:20:20) (□) monolayers.
B, Bem1p (○), OSBP (□), and FAPP1 (▵) were allowed
interact with the POPC/POPE (80:20) monolayer, or Bem1p (•),
OSBP (▪), and FAPP1 (▴) were added to the
POPC/POPE/PtdIns(4)P (77:20:3) monolayer. The subphase consisted
of 10 mm HEPES (pH 7.4) containing 0.16 m KCl. n = 2.
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Figure 6.
Bem1p PX domain in the absence and presence of PS and
PtdIns(4)P.A, C, and E show the electrostatic potential mapped
to the membrane-binding surface of the PX domain. B, D, and F
represent the PX domain as a C-α backbone and the electrostatic
potential as a two-dimensional contour. The molecules are
rotated 90° forward from A, C, and E, and the
membrane-binding surfaces point downward in this orientation.
Even in the absence of lipids (A and B), Tyr^360 is exposed over
the electrostatic potential surface, accounting for the high
intrinsic membrane penetrating activity of Bem1p-PX. Upon
binding to PS (C and D), the electrostatic potential of the
membrane-binding surface of Bem1p-PX is relatively unchanged.
Upon binding to PtdIns(4)P (E and F), the positive electrostatic
potential of the membrane-binding surface of Bem1p-PX is greatly
decreased, exposing Trp^346, which will further penetrate into
the membrane. PtdIns(4)P is colored yellow, and Trp^346 and
Tyr^360 are colored green. PS is not shown.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2007,
282,
25737-25747)
copyright 2007.
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