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Inhibition of mSOS-activity by binding of phosphatidylinositol 4,5-P2 to the mSOS pleckstrin homology domain. 1998

A B Jefferson, and A Klippel, and L T Williams
Chiron Corporation, Emeryville, California 94608, USA.

There are several recently reported examples of inositol phospholipids binding to pleckstrin homology (PH) domains of proteins. The PH domain of SOS, a guanine nucleotide exchange factor for Ras, binds to phosphatidylinositol 4,5 bisphosphate (PtdIns4,5P2). We found that binding of PtdIns4,5P2 to 6-his-tagged recombinant mSOS in vitro inhibits the ability of SOS to catalyze the association of GTP on p21RAS. This inhibition was specific for PtdIns4,5P2: a number of other phosphatidylinositols and phosphatidylserine failed to inhibit Ras GTP-association. We confirmed that the specificity of binding of PtdIns's to recombinant GST-SOS-PH domain is the same as the specificity of PtdIns's for inhibition of SOS activity: namely, that only PtdIns4,5P2 binds significantly to the SOS-PH domain. In addition, the inhibition of Ras GTP-binding is not blocked by excess free inositols suggesting that SOS binds to PtdIns4,5P2 with higher affinity than it binds to free inositols. Addition of SOS-PH domain protein prevented the inhibition of SOS by PtdIns4,5P2 as did addition of the high affinity PtdIns4,5P2-binding drug neomycin. This confirmed that SOS inhibition is mediated by the SOS-PH domain binding to the inositol moiety of PtdIns4,5P2. Binding of Grb2 to SOS did not prevent the inhibition of SOS by PtdIns4,5P2 suggesting that there must be another mechanism for regulating this inhibition. These findings show that the phospholipid PtdIns4,5P2 can suppress the activity of an enzyme involved in signal transduction and suggest that this inhibitory effect must be relieved when SOS is activated.

UI MeSH Term Description Entries
D009355 Neomycin Aminoglycoside antibiotic complex produced by Streptomyces fradiae. It is composed of neomycins A, B, and C, and acts by inhibiting translation during protein synthesis. Fradiomycin Sulfate,Neomycin Palmitate,Neomycin Sulfate
D010750 Phosphoproteins Phosphoprotein
D011506 Proteins Linear POLYPEPTIDES that are synthesized on RIBOSOMES and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of AMINO ACIDS determines the shape the polypeptide will take, during PROTEIN FOLDING, and the function of the protein. Gene Products, Protein,Gene Proteins,Protein,Protein Gene Products,Proteins, Gene
D001798 Blood Proteins Proteins that are present in blood serum, including SERUM ALBUMIN; BLOOD COAGULATION FACTORS; and many other types of proteins. Blood Protein,Plasma Protein,Plasma Proteins,Serum Protein,Serum Proteins,Protein, Blood,Protein, Plasma,Protein, Serum,Proteins, Blood,Proteins, Plasma,Proteins, Serum
D006160 Guanosine Triphosphate Guanosine 5'-(tetrahydrogen triphosphate). A guanine nucleotide containing three phosphate groups esterified to the sugar moiety. GTP,Triphosphate, Guanosine
D001665 Binding Sites The parts of a macromolecule that directly participate in its specific combination with another molecule. Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D016283 Proto-Oncogene Proteins p21(ras) Cellular proteins encoded by the H-ras, K-ras and N-ras genes. The proteins have GTPase activity and are involved in signal transduction as monomeric GTP-binding proteins. Elevated levels of p21 c-ras have been associated with neoplasia. This enzyme was formerly listed as EC 3.6.1.47. Proto-Oncogene Proteins c-ras,c-Ha-ras p21,c-Ki-ras p21,p21(N-ras),p21(c-Ha-ras),p21(c-Ki-ras),p21(c-ras),p21(ras),ras Proto-Oncogene Protein p21,Proto-Oncogene Protein p21(c-Ha-ras),Proto-Oncogene Protein p21(c-Ki-ras),Proto-Oncogene Protein p21(c-N-ras),Proto-Oncogene Protein p21(ras),Proto-Oncogene Protein ras,c-ras Proteins,p21 c-H-ras,p21 c-Ha-ras,p21 c-K-ras,p21 c-Ki-ras,p21 c-ras,ras Proto-Oncogene Product p21,Proteins c-ras, Proto-Oncogene,Proto Oncogene Protein ras,Proto Oncogene Proteins c ras,c Ha ras p21,c Ki ras p21,c ras Proteins,c-H-ras, p21,c-Ha-ras, p21,c-K-ras, p21,c-Ki-ras, p21,c-ras, Proto-Oncogene Proteins,c-ras, p21,p21 c H ras,p21 c Ha ras,p21 c K ras,p21 c Ki ras,p21 c ras,p21, c-Ha-ras,p21, c-Ki-ras,ras Proto Oncogene Product p21,ras Proto Oncogene Protein p21,ras, Proto-Oncogene Protein
D017386 Sequence Homology, Amino Acid The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species. Homologous Sequences, Amino Acid,Amino Acid Sequence Homology,Homologs, Amino Acid Sequence,Homologs, Protein Sequence,Homology, Protein Sequence,Protein Sequence Homologs,Protein Sequence Homology,Sequence Homology, Protein,Homolog, Protein Sequence,Homologies, Protein Sequence,Protein Sequence Homolog,Protein Sequence Homologies,Sequence Homolog, Protein,Sequence Homologies, Protein,Sequence Homologs, Protein
D048868 Adaptor Proteins, Signal Transducing A broad category of carrier proteins that play a role in SIGNAL TRANSDUCTION. They generally contain several modular domains, each of which having its own binding activity, and act by forming complexes with other intracellular-signaling molecules. Signal-transducing adaptor proteins lack enzyme activity, however their activity can be modulated by other signal-transducing enzymes Signal Transducing Adaptor Proteins
D051380 GRB2 Adaptor Protein A signal transducing adaptor protein that links extracellular signals to the MAP KINASE SIGNALING SYSTEM. Grb2 associates with activated EPIDERMAL GROWTH FACTOR RECEPTOR and PLATELET-DERIVED GROWTH FACTOR RECEPTORS via its SH2 DOMAIN. It also binds to and translocates the SON OF SEVENLESS PROTEINS through its SH3 DOMAINS to activate PROTO-ONCOGENE PROTEIN P21(RAS). Growth Factor Receptor-Bound Protein-2,Abundant Src Homology Protein,GRB2 Adaptor Protein, Grb3-3 Isoform,Grb3-3 Adaptor Protein,GRB2 Adaptor Protein, Grb3 3 Isoform,Growth Factor Receptor Bound Protein 2

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