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Figure 2.
FIGURE 2. Structure of the Survivin-Borealin complex. A,
comparison of the overall architecture of the Survivin dimer and
the 1:1 Survivin-Borealin complex. At left is a different view
of the Survivin homodimer than that shown in Fig. 1C, with
monomers shown in purple and blue (Protein Data Bank code 1F3H)
(4). The 2.4-Å structure of Survivin-(1-142) and the
Borealin fragment is shown at center, whereas the 3.3-Å
Survivin-(1-120) structure is shown at right. Survivin is shown
in white, and the Borealin fragment is shown in teal. B,
close-up view of the Survivin dimer interface (far left) and the
corresponding region of the Survivin-(1-142) complex (second
from left). Subunits are colored as described for A. Note the
rearrangement of Survivin side chains to accommodate the
Borealin Trp^70 side chain. The overlay at second from right
illustrates the backbone mimicry by Borealin of the displaced
Survivin monomer, whereas the illustration at far right shows
the Borealin-Survivin backbone overlay in greater detail. The
sequences of the two segments shown at right are
^64ALREMNWLDY^73 (Borealin) and ^92QFEELTLGEF^101 (Survivin).
Colors for the Survivin homodimer and the complex subunits are
as shown in the left two illustrations. C, surface
representation of Survivin showing the pocket that opens up to
accommodate Borealin Trp^70. Borealin is shown as a yellow
ribbon, and the side chain for Tyr^54 is also shown (see
"Results"). The solvent-accessible surface of all Survivin
residues with 4.2 Å of the Trp^70 side chain is colored
blue. The side chains of these Survivin residues are shown as
red sticks. D, comparison of the mode of Borealin recognition
with the typical BIR domain peptide-binding site seen in IAP
proteins. The BIR domains of Survivin and ML-IAP (Protein Data
Bank code 1OXQ) (23) are superimposed (root mean square
deviation = 0.9 Å for structurally conserved BIR domain
heavy atoms). The peptide ligand bound to ML-IAP is shown as
yellow sticks. There is no overlap of IAP-like peptide- and
Borealin-binding sites on the surface of the Survivin monomer.
All structure figures were produced using the program PyMOL (24).
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