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Figure 3.
Fig. 3. The Asn-16-Ala variant of the GCN4 leucine zipper
forms an antiparallel, trimeric coiled coil. (A) Stereo ribbon
diagram of the overall structure. Each helix is colored in
increasingly cool colors from the amino to the carboxyl
terminus. (B) Superpositions of the structures determined by
automated (blue) and manual (yellow) methods in the trigonal
(Left) and tetragonal (Right) crystal forms. (C) Cross section
showing the Ala-16-Leu-12-Leu-12 layer with the van der Waals
surfaces of the core amino acids filling the space in the core
of the trimer. (D) Close packing of the Leu-12-Ala-16-Ala-16
layer. (E) In contrast, a 165-Å3 cavity exists in the
Ala-16 layer of the parallel trimer stabilized by benzene (29).
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