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Figure 2.
Figure 2. Structure and Comparisons of the SAP/SLAM Y281
Complex(A) Surface representation of the SAP domain with the
bound nonphosphorylated peptide shown in green. Hydrophobic
residues at the −1 and −3 positions of the peptide
intercalate with hydrophobic and aromatic residues on the
surface of the domain (see also [D] and Figure 1A). C-terminal
to phosphotyrosine, Val+3 is buried in a mostly hydrophobic
groove.(B) Superposition of the phosphorylated and
nonphosphorylated peptides shows that they adopt an essentially
identical conformation. An alpha-carbon trace of the domain is
shown in gray.(C) Superposition of the unliganded domain (blue)
and the phosphopeptide (yellow) and nonphosphorylated peptide
complexes (green). In the absence of bound peptide, the EF and
BG loops fold inward to close the hydrophobic +3 binding groove.
The conformation of the phosphotyrosine-binding pocket is
essentially the same in all structures. In the unliganded
structure, a sulfate ion occupies the position of the phosphate
group in the phosphopeptide complex.(D) Detail of the
phosphotyrosine-binding pocket in the SLAM/pY281 complex. Red
spheres represent ordered water molecules. The pY281 peptide is
shown in yellow. Thin cyan lines indicate potential hydrogen
bonds. Note that Arg-13 is poorly ordered and does not
participate in phosphotyrosine coordination.(E) Detail of the
phosphotyrosine-binding pocket in the nonphosphorylated
SLAM/Y281 complex. Red spheres represent ordered water
molecules. The Y281 peptide is shown in green. Thin cyan lines
indicate potential hydrogen bonds. Note that Arg-32 organizes an
extensive network of hydrogen bonds in spite of the lack of
phosphorylation of Tyr-281.
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