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PDBsum entry 1cdh
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T-cell surface glycoprotein
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PDB id
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1cdh
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References listed in PDB file
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Key reference
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Title
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Structures of an HIV and mhc binding fragment from human cd4 as refined in two crystal lattices.
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Authors
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S.E.Ryu,
A.Truneh,
R.W.Sweet,
W.A.Hendrickson.
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Ref.
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Structure, 1994,
2,
59-74.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: The T-cell surface glycoprotein CD4 interacts with class II
molecules of the major histocompatibility complex (MHC) enhancing the signal for
T-cell activation. Human CD4 also interacts, at high affinity, with the HIV
envelope glycoprotein, gp120, to mediate T-cell infection by HIV. Crystal
structures of amino-terminal two-domain (D1D2) fragments of human CD4, which
contain the residues implicated in HIV and MHC interactions, have been reported
earlier. RESULTS: We have determined the crystal structure of a new D1D2
construct by molecular replacement from a previously described crystal structure
of D1D2. This structure has more uniform lattice contacts than are in the first.
This gives an improved image of domain D2, which in turn has permitted further
refinement of the initial structure at 2.3 A resolution against a more complete
data set. The structure of the second crystal form was also refined at 2.9 A
resolution. In both models, all residues from 1 to 178 are now well defined,
including the loop regions in D2. CONCLUSIONS: Similarities of the molecular
structure in the two lattices suggest that the D1D2 fragment works as a unit,
with segmental flexibility largely restricted to the junction between domains D2
and D3. Variability of conformation in loops, including those implicated in MHC
and HIV binding, requires an 'induced fit' in these interactions. Well defined
density for the exposed side chain of Phe43 in both crystals confirms a
prominent role for this residue in gp120 binding.
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Figure 4.
Figure 4. B-factor distribution of the refined two crystal
structures, showing B-factors of C[α]atoms. The average
B-factor for all the residues, D1 residues and D2 residues are
29.8 å^2, 23.0 å^2and 38.3 å^2in the type I
crystal form, and 13.7 å^2, 14.7 å^2and 12.5
å^2in the type II crystal form. Figure 4. B-factor
distribution of the refined two crystal structures, showing
B-factors of C[α]atoms. The average B-factor for all the
residues, D1 residues and D2 residues are 29.8 å^2, 23.0
å^2and 38.3 å^2in the type I crystal form, and 13.7
å^2, 14.7 å^2and 12.5 å^2in the type II
crystal form.
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Figure 11.
Figure 11. CDR2-like region implicated in binding interactions.
The region from the C′ C″ β-turn through strand C″ and
into loop C″ D (residues 40–52) is shown from the
superposition of the two structures based on all
C[α]positions. Type I and II structures are shown in red and
blue, respectively. Figure 11. CDR2-like region implicated in
binding interactions. The region from the C′ C″ β-turn
through strand C″ and into loop C″ D (residues 40–52) is
shown from the superposition of the two structures based on all
C[α]positions. Type I and II structures are shown in red and
blue, respectively.
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The above figures are
reprinted
by permission from Cell Press:
Structure
(1994,
2,
59-74)
copyright 1994.
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