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PDBsum entry 2b22
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Biosynthetic protein
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PDB id
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2b22
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References listed in PDB file
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Key reference
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Title
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Antiparallel four-Stranded coiled coil specified by a 3-3-1 hydrophobic heptad repeat.
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Authors
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Y.Deng,
J.Liu,
Q.Zheng,
D.Eliezer,
N.R.Kallenbach,
M.Lu.
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Ref.
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Structure, 2006,
14,
247-255.
[DOI no: ]
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PubMed id
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Abstract
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Coiled-coil sequences in proteins commonly share a seven-amino acid repeat with
nonpolar side chains at the first (a) and fourth (d) positions. We investigate
here the role of a 3-3-1 hydrophobic repeat containing nonpolar amino acids at
the a, d, and g positions in determining the structures of coiled coils using
mutants of the GCN4 leucine zipper dimerization domain. When three charged
residues at the g positions in the parental sequence are replaced by nonpolar
alanine or valine side chains, stable four-helix structures result. The X-ray
crystal structures of the tetramers reveal antiparallel, four-stranded coiled
coils in which the a, d, and g side chains interlock in a combination of
knobs-into-knobs and knobs-into-holes packing. Interfacial interactions in a
coiled coil can therefore be prescribed by hydrophobic-polar patterns beyond the
canonical 3-4 heptad repeat. The results suggest that the conserved, charged
residues at the g positions in the GCN4 leucine zipper can impart a negative
design element to disfavor thermodynamically more stable, antiparallel tetramers.
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Figure 3.
Figure 3. Crystal Structure of the GCN4-pA Tetramer
(A)
Lateral view of the tetramer. Red van der Waals surfaces
identify residues at the a positions, green surfaces identify
residues at the d positions, and yellow surfaces identify
residues at the g positions. The N termini of helices A and B
are indicated.
(B) Axial view of the tetramer. The green,
yellow, and red van der Waals surfaces of the L6 (d), L30 (g),
and V31 (a) side chains are depicted.
(C) Cross-section of
the superhelix in the L20 (d) layer. The 1.5 Å 2F[o] –
F[c] electron density map (contoured at 1.5σ) is shown with the
refined molecular model.
(D) Helical wheel projection of
residues 2–32 of the GCN4-pA tetramer. Heptad repeat positions
are labeled a–g. The leucines at the d positions form the
apolar interface of the tetramer.
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Figure 4.
Figure 4. Crystal Structure of the GCN4-pV Tetramer
(A)
Lateral view of the tetramer. Red van der Waals surfaces
identify residues at the a positions, green surfaces identify
residues at the d positions, and yellow surfaces identify
residues at the g positions. The N termini of helices A and B
are indicated.
(B) Axial view of the tetramer. The green,
yellow, and red van der Waals surfaces of the L6 (d), L30 (g),
and V31 (a) side chains are depicted.
(C) Cross-section of
the superhelix in the L20 (d) layer. The 2F[o] – F[c] electron
density map at 1.2σ contour is shown with the refined molecular
model.
(D) Superposition of the backbone conformations of
the parallel GCN4-pIL tetramer (red) and the antiparallel
GCN4-pA (green) and GCN4-pV (yellow) tetramers.
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The above figures are
reprinted
by permission from Cell Press:
Structure
(2006,
14,
247-255)
copyright 2006.
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