20 research outputs found
Identifying the G protein, G z α
The signalling pathway associated with pertussis and cholera toxin sensitive G proteins have been extensively investigated. In contrast, the function and associated signal transduction cascade for the pertussis toxin insensitive G protein, G(Zα), have remained elusive. Therefore, the aim of this study was to identify the signal transduction pathway associated with G(Zα) by using the protein identification techniques of matrix assisted laser desorption ionization-time of flight mass spectroscopy and N-terminal Edman sequencing. We have chosen this technique to identify proteins that G(Zα) associates with and to gain insights into the potential role this G protein plays in cells. As G(Zα) is predominantly localized in neuronal tissues, homogenates of whole brain tissue were used. G(Zα) and its associated proteins were immunoprecipitated from brain tissue and identified. The immunoprecipitation of four proteins (140, 46, 41 and 36 kDa) was shown to be inhibited in the presence of the G (Zα) peptide. These proteins were subsequently identified as phospholipase C (PLC)-γ, β or γ-actin, G(Zα) and G(β), the β subunit of heterotrimeric G proteins, respectively. These results suggest that G(Zα) exists in a protein complex with the actin cytoskeleton and an important intracellular signalling enzyme, PLC-γ. These methods are powerful techniques for determining protein-protein interactions, and provide the first step to the identification of signalling proteins that G(Zα) associates with. However further experimentation will be required to determine the biological relevance of these protein interactions.</p
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The actin-binding protein profilin binds to PIP2 and inhibits its hydrolysis by phospholipase C
Profilin is generally thought to regulate actin polymerization, but the observation that acidic phospholipids dissociate the complex of profilin and actin raised the possibility that profilin might also regulate lipid metabolism. Profilin isolated from platelets binds with high affinity to small clusters of phosphatidylinositol 4,5-bisphosphate (PIP2) molecules in micelles and also in bilayers with other phospholipids. The molar ratio of the complex of profilin with PIP2 is 1:7 in micelles of pure PIP2 and 1:5 in bilayers composed largely of other phospholipids. Profilin competes efficiently with platelet cytosolic phosphoinositide-specific phospholipase C for interaction with the PIP2 substrate and thereby inhibits PIP2 hydrolysis by this enzyme. The cellular concentrations and binding characteristics of these molecules are consistent with profilin being a negative regulator of the phosphoinositide signaling pathway in addition to its established function as an inhibitor of actin polymerization
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Regulation of phospholipase C-gamma 1 by profilin and tyrosine phosphorylation
Epidermal growth factor and platelet-derived growth factor can stimulate the production of the second messenger inositol trisphosphate in responsive cells, but the biochemical pathway for these signaling events has been uncertain because the reactions have not been reconstituted with purified molecules in vitro. A reconstitution is described that requires not only the growth factor, its receptor with tyrosine kinase activity, and the soluble phospholipase C-gamma 1, but also the small soluble actin-binding protein profilin. Profilin binds to the substrate phosphatidylinositol 4,5-bisphosphate and inhibits its hydrolysis by unphosphorylated phospholipase C-gamma 1. Phosphorylation of phospholipase C-gamma 1 by the epidermal growth factor receptor tyrosine kinase overcomes the inhibitory effect of profilin and results in an effective activation of phospholipase C-gamma 1
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Platelet Glycoprotein IIIa Pl A Polymorphism and Myocardial Infarction
To the Editor:Weiss et al. (April 25 issue)1report an association between thePlA2 allele and the risk of myocardial infarction or unstable angina. Because spurious results are common in studies of allelic associations, additional studies with different sets of data are recommended.2,3We studied the role of this polymorphism in 180 patients with angiographically documented coronary artery disease, including a subgroup of 104 patients with myocardial infarction, and 164 asymptomatic persons who had no history of coronary artery disease and normal physical examinations, electrocardiograms, and echocardiograms. Our results are shown in Table 1.We found no association between . .Â