Purification of recombinant Gi alpha and Go alpha proteins from Escherichia coli.
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Animals↗
Biomedical subjects
M E Linder
Publications and source records attributed to M E Linder.
Purification and characterization of Go alpha and three types of Gi alpha after expression in Escherichia coli.
Complementary DNAs for the G protein alpha subunits Gi alpha 1, Gi alpha 2, Gi alpha 3, and Go alpha were expressed in Escherichia coli, and the four proteins were purified to homogeneity. The recombinant proteins exchange and hydrolyze guanine nucleotide, are ADP-ribosylated by pertussis toxin, and interact with beta gamma subunits. The rates of dissociation of GDP from Gi alpha 1 and Gi alpha 3 (0.03 min-1) are an order of magnitude slower than that from rGo alpha; release of GDP from Gi alpha 2 is also relatively slow (0.07 min-1). However, the values of kcat for the hydrolysis of GTP by rGo alpha and the three rGi alpha proteins are approximately the same, about 2 min-1 at 20 degrees C. The recombinant proteins restore inhibition of Ca2+ currents in pertussis toxin-treated dorsal root ganglion neurons in response to neuropeptide Y and bradykinin, indicating that the proteins can interact functionally with all necessary components of at least one signal transduction system. The two different receptors function with different arrays of G proteins to mediate their responses, since all four G proteins restored responses to bradykinin, while Gi alpha 2 was inactive with neuropeptide Y. Despite these results, high concentrations of activated Gi alpha proteins are without effect on adenylyl cyclase activity, either in the presence or absence of forskolin or Gs alpha, the G protein that activates adenylyl cyclase. These results are consistent with the hypothesis that G protein beta gamma subunits are primarily responsible for inhibition of adenylyl cyclase activity.
Adenosine Diphosphate Ribose↗
TPCK and quercetin act synergistically with vanadate to increase protein-tyrosine phosphorylation in avian cells.
We have found four compounds that act synergistically with the phosphotyrosine phosphatase inhibitor sodium orthovanadate (Na3VO4) to greatly increase the extent of protein-tyrosine phosphorylation in both uninfected chick embryo fibroblasts (CEF) and their Rous sarcoma virus-transformed counterparts (RSV-CEF). These four inhibitors fall into two categories: the chymotrypsin-specific protease inhibitors, tosyl-phenylalanine-chloromethyl ketone (TPCK) and N-carbobenzoxy-1-phenylalanine-chloromethyl ketone (ZPCK); and certain bioflavonoids which can competitively inhibit ATP-binding, quercetin and phloretin.
Amino Acid Chloromethyl Ketones↗
Nonmyristoylated p60v-src fails to phosphorylate proteins of 115-120 kDa in chicken embryo fibroblasts.
We have used anti-phosphotyrosine antibodies to identify a large number of tyrosine phosphoproteins in Rous sarcoma virus (RSV)-transformed chicken embryo fibroblasts. Most of these proteins were found in the 100,000 X g supernatant when cells were separated into soluble and particulate fractions; however, one group of proteins, of 115-120 kDa, was found in the particulate fraction. The phosphotyrosine content of the 115- to 120-kDa proteins was greatly reduced in chicken embryo fibroblasts infected with mutants of RSV (NY314 and SD10) encoding nonmyristoylated forms of the viral src gene product that do not associate with cellular membranes. Since RSV mutants NY314 and SD10 do not transform cells, phosphorylation of this group of 115- to 120-kDa membrane proteins may be related to the process of transformation.
Animals↗
Immunological characterization of proteins detected by phosphotyrosine antibodies in cells transformed by Rous sarcoma virus.
Phosphotyrosine antibodies were used to identify tyrosine-phosphorylated proteins in Rous sarcoma virus (RSV)-transformed chicken embryo fibroblasts. A large number of tyrosine phosphoproteins were detected. A similar set of proteins was observed in RSV-transformed murine cells. An 85,000-dalton protein, however, was present in transformed avian cells but missing in transformed murine cells. Neither the 85,000-dalton protein nor any of the other tyrosine phosphoproteins appeared to be viral structural proteins. Use of RSV mutants encoding partially deleted src gene products enabled us to identify a 60,000-dalton cellular tyrosine phosphoprotein that comigrated with wild-type pp60v-src. With the exception of calpactin I, the major tyrosine phosphoproteins detected in immunoblots appeared to be different from several previously characterized substrates of pp60v-src with similar molecular masses (ezrin, vinculin, and the fibronectin receptor).
Annexins↗
A similar ribosomal protein S6 kinase activity is found in insulin-treated 3T3-L1 cells and chick embryo fibroblasts transformed by Rous sarcoma virus.
Insulin and transformation by Rous sarcoma virus stimulate the phosphorylation of ribosomal protein S6. Soluble fractions containing activated S6 protein kinase from insulin-treated cells and from transformed chick embryo fibroblasts were compared. Based upon several characteristics notably elution from DEAE-cellulose and sedimentation in glycerol gradients, these two S6 protein kinase activities appear to be similar enzymes. Thus insulin and retroviral transformation may activate the same enzyme to regulate the phosphorylation state of S6.
Animals↗
Jakob-Creutzfeldt disease-EEG observations with special reference to occurrence of complexes and their relationship to other body events.
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Central Nervous System Diseases↗