Mastoparan, a peptide toxin from wasp venom, causes the activation of GTP- binding regulatory proteins (G proteins) by promoting GTP binding in a manner strikingly similar to that of cell surface receptors. mastoparan (MP), a cationic, amphiphilic helix, is also structurally similar to putative G protein-binding domains on these receptors. I propose to study the mechanism and structural basis of the G protein activation by MP and related amphiphilic compounds as a model for receptor-G protein coupling and to develop G protein-specific regulatory peptides as probes of cellular regulation. (1) We will develop MP analogs that are more potent and more selective G protein activators and inhibitors. Structure-activity analysis will use kinetic assays with purified G proteins and recombinant alpha subunits, physical studies of MP-G protein complexes, and computer assisted modeling. (2) Affinity cross-linking between MP and G proteins will be performed to determine the MP-binding site, presumably the receptor binding-site as well. We will evaluate competition between receptor and MP for binding to G proteins to evaluate the identity of their binding sites. (3) Circular dichroism, 19F-NMR, and fluorescence spectroscopy will be used to study the structural basis of MP-G protein binding. Two-dimensional transferred NOE of 1H-NMR (500 MHz) will be used to determine the conformation of MP when bound to G proteins. The conformational basis of MP binding to G proteins will be compared with its binding to calmodulin, which binds many amphiphilic peptides. (4) We will study the mechanism by which MP and related compounds activate G proteins or block activation using kinetic and ligand binding assays. We will clarify the roles of the G protein betagamma subunits and Mg2+ on MP action. We will extend these studies to small GTP-binding proteins, particularly p21ras, which are not known to be regulated by receptors. (5) MP analogs will be used to study G protein-mediated signaling in cells. Affinity crosslinking of MP targets in cells, measurements of MP uptake and its mechanism and the use of MP as an affinity chromatographic ligand will be included in these experiments.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM040676-02
Application #
3298454
Study Section
Physiological Chemistry Study Section (PC)
Project Start
1989-12-01
Project End
1992-11-30
Budget Start
1990-12-01
Budget End
1991-11-30
Support Year
2
Fiscal Year
1991
Total Cost
Indirect Cost
Name
University of Texas Sw Medical Center Dallas
Department
Type
Schools of Medicine
DUNS #
City
Dallas
State
TX
Country
United States
Zip Code
75390
Sukumar, M; Ross, E M; Higashijima, T (1997) A Gs-selective analog of the receptor-mimetic peptide mastoparan binds to Gs alpha in a kinked helical conformation. Biochemistry 36:3632-9
Okada, A; Wakamatsu, K; Miyazawa, T et al. (1994) Vesicle-bound conformation of melittin: transferred nuclear Overhauser enhancement analysis in the presence of perdeuterated phosphatidylcholine vesicles. Biochemistry 33:9438-46
Ross, E M; Higashijima, T (1994) Regulation of G-protein activation by mastoparans and other cationic peptides. Methods Enzymol 237:26-37
Mukai, H; Higashijima, T (1993) Inhibitory effects of substance P analogs on the activation of GTP-binding regulatory proteins by receptors. Regul Pept 46:338-9
Antonny, B; Sukumar, M; Bigay, J et al. (1993) The mechanism of aluminum-independent G-protein activation by fluoride and magnesium. 31P NMR spectroscopy and fluorescence kinetic studies. J Biol Chem 268:2393-402
Mukai, H; Munekata, E; Higashijima, T (1992) G protein antagonists. A novel hydrophobic peptide competes with receptor for G protein binding. J Biol Chem 267:16237-43
Wakamatsu, K; Okada, A; Miyazawa, T et al. (1992) Membrane-bound conformation of mastoparan-X, a G-protein-activating peptide. Biochemistry 31:5654-60
Sukumar, M; Higashijima, T (1992) G protein-bound conformation of mastoparan-X, a receptor-mimetic peptide. J Biol Chem 267:21421-4
Higashijima, T; Graziano, M P; Suga, H et al. (1991) 19F and 31P NMR spectroscopy of G protein alpha subunits. Mechanism of activation by Al3+ and F-. J Biol Chem 266:3396-401
Hazlett, T L; Higashijima, T; Jameson, D M (1991) Examination of elongation factor Tu for aluminum fluoride binding sites using fluorescence and 19F-NMR methodologies. FEBS Lett 278:225-8

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