A 50 kDa Protein Modulates Guanine Nucleotide Binding of Transglutaminase II
| Autor: | Shailesh Y. Desai, Mie-Jae Im, Tanya Das, Kwang Jin Baek, Caroline D. Gray, Michael Ludwig, Ratan Gacchui, Ki-Chul Hwang |
|---|---|
| Rok vydání: | 1996 |
| Předmět: |
GTP'
Guinea Pigs Down-Regulation Alpha (ethology) GTPase In Vitro Techniques Guanosine Diphosphate Biochemistry GTP Phosphohydrolases GTP-Binding Proteins Animals Beta (finance) Receptor Ternary complex Transglutaminases Chemistry Activator (genetics) Proteins Heterotetramer Molecular biology Guanine Nucleotides Molecular Weight Liver Guanosine 5'-O-(3-Thiotriphosphate) Guanosine Triphosphate Protein Binding Signal Transduction |
| Zdroj: | Biochemistry. 35:2651-2657 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/bi9522965 |
| Popis: | Regulation of cellular response is an important mechanism for controlling cellular functions. The transmembrane signaling of the hormone receptors is regulated by GTP-binding proteins (GTPases) and their associated proteins. Our previous studies demonstrated that the bifunctional GTP-binding protein, G alpha h (transglutaminase II), consistently copurified with an approximately 50 kDa protein (G Beta h) which is dissociated from G alpha h upon activation with GTP gamma S or AlF4-. Present immunological and biochemical studies on the regulation of the GTPase cycle of G alpha h, which involves the alpha 1-adrenoceptor and 50 KDa G beta h, reveal that the 50 kDa protein is indeed a G alpha h-associated protein and down regulates functions of G alpha h. Thus, polyclonal antibody against G Beta h coimmunoprecipitates GDP-bound G alpha h but not the GDP-AlF4--bound form. The GTP gamma S binding and GTPase activity of G alpha h are inhibited in a G beta h concentration dependent manner. Supporting this notion, G beta h accelerated GTP gamma S release from G alpha h and changes the affinity of G alpha h from GTP to GDP. Moreover, the ternary complex preparation exhibits TGase activity that is inhibited in the presence of the alpha 1-agonist and GTP. The GTP gamma S binding by the ternary complex, consisting of the alpha 1-agonist, the receptor, and Gh, is also inhibited by G beta h. The inhibition of GTP gamma S binding with the ternary complex requires a > or = 2.7-fold higher concentration of G beta h than the G alpha h alone, indicating that the receptor enhances the affinity of G alpha h for GTP. In addition, G beta h copurifies with an alpha 1-agonist, adrenoceptor, and G alpha h ternary complex, showing that the complex is a heterotetramer. Our data also suggest that G beta h does not directly interact with alpha 1-adrenoceptor. These findings clearly demonstrate that G alpha h associates with a novel protein which modulates the affinity of G alpha h for guanine nucleotides and that the GDP-bound Gh is the ground state for the counterpart activator, the alpha 1-adrenoceptor, in this signaling system. |
| Databáze: | OpenAIRE |
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