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M94A0306.TXT
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1994-10-08
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Document 0306
DOCN M94A0306
TI Structures of an HIV and MHC binding fragment from human CD4 as refined
in two crystal lattices.
DT 9412
AU Ryu SE; Truneh A; Sweet RW; Hendrickson WA; Department of Biochemistry
and Molecular Biophysics, Columbia; University, New York, NY 10032.
SO Structure. 1994 Jan 15;2(1):59-74. Unique Identifier : AIDSLINE
MED/94356446
AB 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.
DE Amino Acid Sequence Antigens, CD/*CHEMISTRY/METABOLISM Antigens,
CD4/*CHEMISTRY/METABOLISM Binding Sites Calorimetry Computer Graphics
Crystallography, X-Ray/METHODS Human Hydrogen Bonding HIV/*METABOLISM
*Major Histocompatibility Complex Models, Molecular Molecular Sequence
Data Peptide Fragments/*CHEMISTRY/METABOLISM *Protein Conformation
Software Support, U.S. Gov't, Non-P.H.S. JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).