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Figure 4.
FIGURE 4. Mapping of two potential sites on Kal-SH3 for
binding of intramolecular PXXP motifs. A, molecular surface
representations of Kal-SH3 showing residues affected upon
interaction with various PXXP peptides. The lower surface plots
represent an 180° rotation about the z axis of the upper
surface plots. Residues showing chemical shifts upon interaction
with the PXXP peptide are colored as follows. Background was
defined as the maximal chemical shift observed for residues in
the N and C termini, which are disorderedand should not change
upon ligand binding. Residues colored blue have chemical shift
changes of >0.05 ppm for the PLSP peptide and >0.14 ppm for the
PKTP peptide and represent site 1. Residues colored green have
chemical shift changes of >0.14 ppm for the PKTP peptide and
>0.06 ppm for the PLPP peptide and represent site 2. Changes in
chemical shifts not colored in this figure are Val^21 and Ser^63
for the PLSP peptide and Glu^67 for the PKTP peptide. The
canonical PXXP-binding site mapped in other SH3 structures is
shown on the far right (colored magenta) B, alignment of Kalirin
and Trio N-terminal SH3 domains from different species (upper)
with SH3 domains of defined structure with canonical
ligand-binding sites (middle) and non-canonical binding sites
(lower). The frog Kalirin sequence is derived from an expressed
sequence tag that is missing the N-terminal SH3 domain sequence
(dashes). The secondary structure of Kal-SH3 is indicated above
the sequences and is color-coded as described in the legend to
Fig. 2. Kalirin residues that show chemical shift changes of
>0.15 ppm upon binding of the PKTP peptide (330 µM) to the
SH3 domain (590 µM) are colored blue for site 1 and green
for site 2. Numbering is as for the structural determination of
the SH3 domain. Residues colored magenta are ligand-binding
residues observed in the structures of Fyn (Protein Data Bank
code 1AON), c-Src (code 1NLP), Abl (code 1ABO),  -spectrin ( -sp;
code 1HD3), Grb2 (N terminus; code 1AZE), c-Crk (N terminus;
code 1CKA), Sem5 (C terminus; code 2SEM), GADS (code 1H3H),
p67^phox (code 1K4U), Pex13p (code 1NM7), Grb2 (C terminus; code
1GFC), and Vav1 (code 1GCQ).
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