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PDBsum entry 1a22
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Complex (hormone/receptor)
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PDB id
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1a22
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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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Structural and functional analysis of the 1:1 growth hormone:receptor complex reveals the molecular basis for receptor affinity.
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Authors
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T.Clackson,
M.H.Ultsch,
J.A.Wells,
A.M.De vos.
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Ref.
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J Mol Biol, 1998,
277,
1111-1128.
[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 were identified by an automated
search of PubMed on title and author
names, giving a
perfect match.
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Abstract
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The designed G120R mutant of human growth hormone (hGH) is an antagonist and can
bind only one molecule of the growth hormone receptor. We have determined the
crystal structure of the 1:1 complex between this mutant and the receptor
extracellular domain (hGHbp) at 2.6 A resolution, and used it to guide a
detailed survey of the structural and functional basis for hormone-receptor
recognition. The overall structure of the complex is very similar to the
equivalent portion of the 1:2 complex, showing that formation of the active
complex does not involve major conformational changes. However, a segment
involved in receptor-receptor interactions in the 1:2 complex is disordered in
this structure, suggesting that its productive conformation is stabilized by
receptor dimerization. The hormone binding site of the receptor comprises a
central hydrophobic patch dominated by Trp104 and Trp169, surrounded by a
hydrophilic periphery containing several well-ordered water molecules. Previous
alanine scanning showed that the hydrophobic "hot spot" confers most of the
binding energy. The new structural data, coupled with binding and kinetic
analysis of further mutants, indicate that the hot spot is assembled
cooperatively and that many residues contribute indirectly to binding. Several
hydrophobic residues serve to orient the key tryptophan residues; kinetic
analysis suggests that Pro106 locks the Trp104 main-chain into a required
conformation. The electrostatic contacts of Arg43 to hGH are less important than
the intramolecular packing of its alkyl chain with Trp169. The true functional
epitope that directly contributes binding energy may therefore comprise as few
as six side-chains, participating mostly in alkyl-aromatic stacking
interactions. Outside the functional epitope, multiple mutation of residues to
alanine resulted in non-additive increases in affinity: up to tenfold for a
hepta-alanine mutant. Contacts in the epitope periphery can therefore attenuate
the affinity of the central hot spot, perhaps reflecting a role in conferring
specificity to the interaction.
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Figure 3.
Figure 3. Stereo views of selected receptor-hGH
interactions. In these panels, the receptor is colored green and
hGH in red, water molecules are shown as red spheres, and broken
lines represent hydrogen bonds. Alanine mutagenesis studies
reveal that the pockets shown in (a) and (b) contain side-chains
that are critical for high-affinity binding, whereas side-chain
interactions shown in (c) and (d) have little effect on binding.
(a) The binding pocket for Trp104. Loop EF[N] (residues 101 to
106) of the receptor interacts with residues on helix 4 (168 to
176) and 60 to 63 of hGH. A well-ordered water molecule (B=24
Å^2) bridges between the carbonyl atoms of residues Ser102
and Pro106 and the amide of Ile105. (b) The binding pocket for
Trp169. Trp169 of loop BC[C] and Arg43 of loop AB[N] interact
with residues 171 to 179 of helix 4 of hGH, as well as with the
second minihelix (residues 64 to 68). Several water molecules
are found near the periphery of the pocket (with B-factors
varying between 19 and 49 Å^2). (c) Interactions between
the first minihelix of hGH (residues 41 to 48) and the
solvent-exposed face of the CC′FG sheet of the N-terminal
domain of the receptor. (d) Interactions between residues on
helix 1 of hGH and loop FG[C] of the receptor. No intermolecular
hydrogen bonds are found; Glu174 of the hormone interacts with
histidine residues 18 and 21.
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Figure 6.
Figure 6. Residues surrounding Trp104 and Trp169
side-chains. Arg43 makes electrostatic interactions to hGH but
also packs closely with Trp169. Ile103 packs against the
side-chain of Trp104.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(1998,
277,
1111-1128)
copyright 1998.
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Secondary reference #1
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Title
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Crystals of human growth hormone-Receptor complexes. Extracellular domains of the growth hormone and prolactin receptors and a hormone mutant designed to prevent receptor dimerization.
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Authors
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M.Ultsch,
A.M.De vos.
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Ref.
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J Mol Biol, 1993,
231,
1133-1136.
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PubMed id
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