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Figure 3.
Figure 3. Crystal Structure of Sec23•Sar1 Complexed with
the Active Fragment of Sec31
The ribbon representation is
shown with the membrane-distal surface of the complex facing
forward. Sec23 is orange and Sar1 is red. The Sec31 active
fragment is in five colors: the N-terminal element that
interacts solely with Sar1 (purple, residues 907–920); a short
element that interacts with both Sec23 and Sar1 residues at the
interface (white, residues 920–922); two elements that
interact with Sec23 (blue, residues 923–927; green, residues
935–942); and the intervening stretch that interacts loosely
with Sec23 (yellow, residues 928–934). The blue contour lines
show difference electron density calculated prior to the
inclusion of the Sec31 active fragment (at 2.5 Å
resolution, contoured at 2.9 σ). Domains of the Sec23 protein
are labeled, and the interface with Sec24 is indicated at the
bottom of the picture. The switch 2 (labeled Sw2) and helix α3
elements of Sar1 to which Sec31 binds are indicated.
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