D. Cussac et al., BINDING OF THE GRB2 SH2 DOMAIN TO PHOSPHOTYROSINE MOTIFS DOES NOT CHANGE THE AFFINITY OF ITS SH3 DOMAINS FOR SOS PROLINE-RICH MOTIFS, EMBO journal, 13(17), 1994, pp. 4011-4021
Phosphotyrosine peptide binding to Grb2 induces tryptophan fluorescenc
e changes in the Src homology 2 (SH2) domain. Affinities are in the na
nomolar range, the She peptide having the highest affinity, followed b
y peptides mimicking Grb2 binding sites on EGF and HGF receptors, the
putative sites on insulin and IGF-1 receptors having much lower affini
ties. Proline-rich peptide binding to the SH3 domains induces fluoresc
ence changes mainly in the C-terminal SH3. Affinities are in the micro
molar range, the highest affinity peptides mimicking the first proline
-rich motif of the Sos C-terminus. Additional residues before this PVP
PPVPP motif provide a minor contribution to the binding, but the two r
esidues after this motif are important and may contribute to specifici
ty. The affinity of each SH3 for each proline-rich motif is too low to
account for the high stability of the Grb2-Sos complex, suggesting th
at Grb2 recognizes other structural features in the Sos C-terminus. Bi
nding of a phosphotyrosine peptide to the SH2 has no effect on the SH3
s. Thus the binding of Grb2 to a receptor or to an associated protein
phosphorylated on tyrosines is unlikely to activate the exchange facto
r activity of Sos through a conformational change transmitted from the
SH2 to the SH3 domains.