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Figure 3.
Figure 3. (a) Superposition of the minimized average
structures of the cis SH2 domain (orange), the trans SH2 domain
(light blue) and the phospholigand-bound SH2 domain (dark blue).
The phospholigand is shown in red and the pY and pY+3 residues
are labeled. The BG loop is indicated and the arrow shows the
shift in position of the alpha carbon atom of Leu329 that
accompanies isomerization of Pro287 from the cis to trans
conformations. The structure of the BG loop for the
phospholigand-bound SH2 domain (dark blue) is similar to that of
BG loop in the ligand-free trans domain (light blue). (b)
Superposition of the lowest energy structures of the Itk cis SH2
domain (20 structures), the trans SH2 domain (20 structures) and
the SH2/phosphopeptide complex (20 structures). Colors
correspond to those in (a). The ensemble of structures indicates
that the BG loop in the cis SH2 structure (orange) adopts a
range of conformations that differ from the conformational
preferences of both the trans SH2 domain and the phospholigand
bound SH2 domain. For both (a) and (b) backbone heavy atoms
within the secondary structural elements were used for
superpositions.
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