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PDBsum entry 4fab
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Immunoglobulin
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PDB id
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4fab
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Three-Dimensional structure of a fluorescein-Fab complex crystallized in 2-Methyl-2,4-Pentanediol.
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Authors
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J.N.Herron,
X.M.He,
M.L.Mason,
E.W.Voss,
A.B.Edmundson.
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Ref.
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Proteins, 1989,
5,
271-280.
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PubMed id
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Abstract
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The crystal structure of a fluorescein-Fab (4-4-20) complex was determined at
2.7 A resolution by molecular replacement methods. The starting model was the
refined 2.7 A structure of unliganded Fab from an autoantibody (BV04-01) with
specificity for single-stranded DNA. In the 4-4-20 complex fluorescein fits
tightly into a relatively deep slot formed by a network of tryptophan and
tyrosine side chains. The planar xanthonyl ring of the hapten is accommodated at
the bottom of the slot while the phenylcarboxyl group interfaces with solvent.
Tyrosine 37 (light chain) and tryptophan 33 (heavy chain) flank the xanthonyl
group and tryptophan 101 (light chain) provides the floor of the combining site.
Tyrosine 103 (heavy chain) is situated near the phenyl ring of the hapten and
tyrosine 102 (heavy chain) forms part of the boundary of the slot. Histidine 31
and arginine 39 of the light chain are located in positions adjacent to the two
enolic groups at opposite ends of the xanthonyl ring, and thus account for
neutralization of one of two negative charges in the haptenic dianion. Formation
of an enol-arginine ion pair in a region of low dielectric constant may account
for an incremental increase in affinity of 2-3 orders of magnitude in the 4-4-20
molecule relative to other members of an idiotypic family of monoclonal
antifluorescyl antibodies. The phenyl carboxyl group of fluorescein appears to
be hydrogen bonded to the phenolic hydroxyl group of tyrosine 37 of the light
chain. A molecule of 2-methyl-2,4-pentanediol (MPD), trapped in the interface of
the variable domains just below the fluorescein binding site, may be partly
responsible for the decrease in affinity for the hapten in MPD.
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Secondary reference #1
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Title
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Differences in crystal properties and ligand affinities of an antifluorescyl FAB (4-4-20) in two solvent systems.
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Authors
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A.L.Gibson,
J.N.Herron,
X.M.He,
V.A.Patrick,
M.L.Mason,
J.N.Lin,
D.M.Kranz,
E.W.Voss,
A.B.Edmundson.
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Ref.
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Proteins, 1988,
3,
155-160.
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PubMed id
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