title: Differential interactions of human Sos1 and Sos2 with Grb2.
abstract: The guanine nucleotide exchange factor Son of sevenless (Sos) performs a crucial step in the coupling of receptor tyrosine kinases to Ras activation. Mammalian cells contain two related but distinct Sos proteins, Sos1 and Sos2. Although they share a high degree of overall similarity, it is not known to what extent their biological and biochemical properties overlap. In the present study, we have compared the interactions of the two human homologues of Sos, hSos1 and hSos2, with the adaptor protein Grb2. We show that hSos2 interacts with Grb2 via its proline-rich COOH-terminal domain and that this interaction is dependent on the SH3 domains of Grb2. In general, these characteristics are similar to the ones reported previously for the interaction of hSos1 with Grb2. However, the apparent binding affinity of hSos2 for Grb2 is significantly higher relative to that of hSos1 both in vitro and in vivo. The region conferring this higher binding affinity has been mapped to residues 1126-1242 of the hSos2 COOH-terminal domain. These results suggest that Sos1 and Sos2 may differentially contribute to receptor-mediated Ras activation.
authors.affiliation: Department of Molecular Genetics and Microbiology, School of Medicine, State University of New York, Stony Brook 11794, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Yang
authors.forename: L
authors.initials: L
authors.lastname: Van Aelst
authors.forename: D
authors.initials: D
authors.lastname: Bar-Sagi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D001483:Base Sequence; D051380:GRB2 Adaptor Protein; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D015151:Immunoblotting; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020664:Son of Sevenless Proteins; D020663:ras Guanine Nucleotide Exchange Factors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D020664:Son of Sevenless Proteins; D020663:ras Guanine Nucleotide Exchange Factors