IndraLab

"Herein, we have provided compelling evidence that the binding of Sos1 and Gab1 to Grb2 in a non-competitive manner to generate the Sos1-Grb2-Gab1 ternary signaling complex employs an allosteric mechanism."

"While we have relied here on short peptides to mimic Sos1 and Gab1, due largely to inherent difficulties associated with isolation and purification of full-length Sos1 and Gab1 proteins, it should be noted that these peptides suffice par excellence for studying the binding of Sos1 and Gab1 to Grb2 using biophysical methods."

"FRS2 was originally discovered as a docking site for coordinated assembly of a multiprotein complex that includes GRB2, GAB1, and SOS1, and serves a critical role in the FGFR signaling pathway (Sato and Gotoh xref )."

"On the contrary, our previous work has shown that the formation of Sos1-Grb2-Gab1 ternary complex is under tight allosteric control [ xref ]."

"As shown in xref , it is clearly evident that the stoichiometries and energetics of binding of Sos1 and Gab1 peptides to Grb2 in Tris buffer versus Phosphate buffer are virtually indistinguishable."

"It is also of worthy note that the binding of both the Sos1 and Gab1 peptides to Grb2 is largely driven by favorable enthalpic contribution accompanied by entropic penalty ( xref and xref )."

"FRS2 was originally discovered as a docking site for coordinated assembly of a multi-protein complex that includes GRB2, GAB1, and SOS1 and serves a critical role in the FGFR signaling pathway ( xref )( xref , xref )."

"Moreover, KIF26A did not affect Grb2 binding to Sos1 or Gab1 (M)."

"Although these CD measurements are of highly qualitative nature and thus do not provide the physical basis of how the binding of Sos1 to the nSH3 domain may trigger a conformational change within Grb2 such that the nSH3 domain is only accessible to Gab1, the fact that Grb2 appears to be a highly flexible molecule by virtue of its ability to undergo discernable secondary and tertiary structural changes upon binding to Sos1 and Gab1 peptides nonetheless supports the notion that allostery is likely to play a central role in mediating communication between the nSH3 and cSH3 domains so as to allow the assembly of Sos1-Grb2-Gab1 ternary signaling complex in a non-competitive manner."

"This plausible scenario was however cut short by the demonstration that Sos1 and Gab1 do not compete for Grb2 but rather associate in a mutually inclusive manner leading to the formation of the Sos1-Grb2-Gab1 ternary signaling complex [ xref ]."

"Grb2 binds to both the Sos1 and Gab1 peptides with a 1:1 stoichiometry."

"Stimulation with FGFs causes SNT-1/FRS2 phosphorylation and its binding to FGFRs via the phosphotyrosine-binding domain, which consequently leads to activation of downstream signaling pathways through its interaction with adaptor proteins GRB2, GAB1 and SOS1 [ xref ]."

"In light of these considerations, one would expect the binding of Sos1 and Gab1 peptides to full-length Grb2 with stoichiometries of 2:1 and 1:1, respectively."

"Given that the formation of Sos1-Grb2-Gab1 ternary signaling complex proceeds in a non-competitive manner [ xref ], the most straightforward interpretation of these salient observations is that the Sos1 peptide binds only to the nSH3 domain but not the cSH3 domain, while the Gab1 peptide binds only to the cSH3 domain in the context of full-length Grb2."

"Although efforts by others and us directed at the determination of X-ray or NMR structures of full-length Grb2 bound to Sos1 or Gab1 constructs of any sort over the past decade or so have met no success, presumably due to the transient nature of Sos1-Grb2-Gab1 complex, we have nonetheless made an attempt here to create a crude 3D structural model of how the binding of one molecule of Sos1 to the nSH3 domain may allosterically induce a conformational change within Grb2 such that the loading of a second molecule of Sos1 onto the cSH3 domain is blocked and, in so doing, allowing Gab1 access to the cSH3 domain in an exclusively non-competitive manner to generate the Sos1-Grb2-Gab1 ternary complex ( xref )."

"The phosphatase activity of SHP2 is required for the formation of the GAB1–GRB2–SOS1 complex, which in turn promotes RAS activation xref (Fig. xref )."

"It dephosphorylates the inhibitory pY32 on RAS to enhance RAS activation (Bunda et al., 2015; Liotti et al., 2021), dephosphorylates GAPs like RASA to stabilize GTP-RAS (Bunda et al., 2015), and binds to the GAB1-GRB2-SOS1 complex at the membrane to facilitate their GEF function and increase levels of GTP-RAS (Nichols et al., 2018)."