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Figure 3.
Fig. 3. DSS1 binds BRCA2 in an extended conformation,
interacting with basic grooves on the helical domain, OB1 and
OB2 domains. (A) The NH[2]-terminal segment of DSS1 (orange)
tunnels through the helical domain (magenta), and also contacts
OB1 (green). View is rotated ~180° about the horizontal axis
relative to Fig. 1D. In addition to the contacts discussed in
the text, Glu14 of DSS1 interacts with Lys2712 of OB1, Glu15
with Gln2576, Asp16 with Lys2671, Asp17 with Lys2551, and Glu18
with Lys2435 and Arg2441. In addition, Asp16 forms a salt bridge
with Arg57, located on the COOH-terminal DSS1 segment that binds
on the opposite side of BRCA2. (B) Surface representation of the
helical domain-OB1 region that binds the NH[2]-terminal segment
of DSS1, in an orientation similar to that of (A). The surface
is colored according to the electrostatic potential (-30 kT to
+30 kT), calculated in the absence of DSS1 with the program
GRASP (92). The backbone traces of the NH[2]-terminal and part
of the COOH-terminal DSS1 segments are shown as white coils, and
the side chains, in yellow. The white-dotted line indicates the
11-residue disordered segment between the NH[2]- and
COOH-terminal segments of DSS1. DSS1 residues that are entirely
buried below the surface of BRCA2 are indicated in parenthesis.
The side chains for residues 46 to 49 of the COOH-terminal
segment have poor electron density and are omitted. (C) Surface
representation of the helical domain-OB1-OB2 region that binds
the COOH-terminal segment of DSS1, in an orientation rotated
~90° about the vertical axis relative to (B). Hydrophobic
interactions include the DSS1 Phe^19, Trp39, Trp43, which pack
with Trp2646, Phe^2722, and with an opening in the hydrophobic
core of OB1, respectively. In addition, the majority of the
acidic DSS1 residues are near clusters of basic BRCA2 residues.
These include Glu40, Asp41, and Asp44, which are near Arg2708,
Lys2898, and Lys2655; Asp50 and Asp51, which are near Arg2708
and Arg2451; and Glu20 and Glu21 [from the NH[2]-terminal
segment in (B)] which are near Lys2712, Arg2717, Arg2590 and
Lys2595.
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