Guanine-nucleotide binding proteins (G proteins) act as molecular switches in signaling pathways, by coupling the activation of G protein-coupled receptors (GPCRs) at the cell surface to intracellular responses. In the resting state, G protein forms a heterotrimer, consisting of GDP-bound form of the G protein α subunit (Gα(GDP)) and G protein βγ subunit (Gβγ). Ligand binding to GPCRs promotes the GDP-GTP exchange on Gα, leading to the dissociation of the GTP-bound form of Gα (Gα(GTP)) and Gβγ. Then, Gα(GTP) and Gβγ bind to their downstream effector enzymes or ion channels and regulate their activities, leading to a variety of cellular responses. Finally, Gα hydrolyzes the bound GTP to GDP and returns to the resting state by re-associating with Gβγ. G proteins are classified with four major families based on the amino acid sequences of Gα: i/o, s, q/11, and 12/13. Each family transduces the signaling from different GPCRs to the specific effectors. Here, we established the backbone resonance assignments of human Gαi3, a member of the i/o family, with a molecular weight of 41 K in complex with a GTP analogue, GTPγS.
Heterotrimeric guanine-nucleotide binding protein G protein α subunit Signal transduction GPCR-signaling
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This work was supported in part by grants from the Japan New Energy and Industrial Technology Development Organization (NEDO) and the Ministry of Economy, Trade, and Industry (METI) (to I. S.), a grant-in-aid for Scientific Research on Priority Areas from the Japanese Ministry of Education, Culture, Sports, and Technology (MEXT) (to M. O. and I. S.), Global COE Program “Medical System Innovation on Multidisciplinary Integration” from MEXT (to Y. M.), and a grant from Takeda Science Foundation (to M. O.). Y. M. is a research fellow of the Japan Society of Promotion of Science (JSPS).
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