• Journal of Life Science
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• v.20 no.8
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• pp.1166-1172
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• 2010

Kinesin-I exists as a tetramer of two heavy chains (KHCs, also called KIF5s), which contain the amino (N)-terminal motor domain and carboxyl (C)-terminal domain, as well as two light chains (KLCs), which bind to the KIF5s (KIF5A, KIF5B and KIF5C) stalk region. To identify the interaction proteins for KIF5A, yeast two-hybrid screening was performed and a specific interaction with the ${\beta}$ subunit of heterotrimeric G proteins ($G{\beta}$) was found. $G{\beta}$ bound to the amino acid residues between 808 and 935 of KIF5A and to other KIF5 members in the yeast two-hybrid assay. The WD40 repeat motif of $G{\beta}$ was essential for interaction with KIF5A. In addition, these proteins showed specific interactions in the glutathione S-transferase (GST) pull-down assay. An antibody to KIF5s specifically co-immunoprecipitated KIF5s associated with heterotrimeric G proteins from mouse brain extracts. These results suggest that kinesin-I motor protein transports heteroterimeric G protein attachment vesicles along microtubules in the cell.

• Journal of Microbiology
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• v.44 no.2
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• pp.145-154
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• 2006

Heterotrimeric G proteins (G proteins) are conserved in all eukaryotes and are crucial components sensing and relaying external cues into the cells to elicit appropriate physiological and biochemical responses. Basic units of the heterotrimeric G protein signaling system include a G protein-coupled receptor (GPCR), a G protein composed of ${\alpha},\;{\beta},\;and\;{\gamma}$ subunits, and variety of effectors. Sequential sensitization and activation of these G protein elements translates external signals into gene expression changes, resulting in appropriate cellular behaviors. Regulators of G protein signaling (RGSs) constitute a crucial element of appropriate control of the intensity and duration of G protein signaling. For the past decade, G protein signaling and its regulation have been intensively studied in a number of model and/or pathogenic fungi and outcomes of the studies provided better understanding on the upstream regulation of vegetative growth, mating, development, virulence/pathogenicity establishment, and biosynthesis of secondary metabolites in fungi. This review focuses on the characteristics of the basic upstream G protein components and RGS proteins, and their roles controlling various aspects of biological processes in the model filamentous ascomycete fungus Aspergillus nidulans. In particular, their functions in controlling hyphal proliferation, asexual spore formation, sexual fruiting, and the mycotoxin sterigmatocystin production are discussed.

• BMB Reports
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• v.34 no.2
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• pp.95-101
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• 2001

Tissue transglutaminase (TGII, $G{\alpha}h$) belongs to a family of enzymes which catalyze post-translational modification of proteins by forming isopeptides via $Ca^{2+}$-dependent reaction. Although TGII-mediated formation of isopeptides has been implicated to play a role in a variety of cellular processes, the physiological function of TGII remains unclear. In addition to this Tease activity, TGII is a guanosine triphosphatase (GTPase) which binds and hydrolyzes GTP It is now well recognized that the GTPase action of TGII regulates a receptor-mediated transmembrane signaling, functioning as a signal transducer of the receptor. This TGII function signifies that TGII is a new class of GTP-binding regulatory protein (G-protein) that differs from "Classical" heterotrimeric G-proteins. Regulation of enzyme is an important biological process for maintaining cell integrity. This review summarizes the recent development in regulation of TGII that may help for the better understanding of this unique enzyme. Since activation and inactivation of GTPase of TGII are similar to the heterotrimeric G-proteins, the regulation of heterotrimeric G-protein in the transmembrane signaling is also discussed.

• Biomolecules & Therapeutics
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• v.25 no.1
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• pp.4-11
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• 2017

Heterotrimeric G proteins are key intracellular coordinators that receive signals from cells through activation of cognate G protein-coupled receptors (GPCRs). The details of their atomic interactions and structural mechanisms have been described by many biochemical and biophysical studies. Specifically, a framework for understanding conformational changes in the receptor upon ligand binding and associated G protein activation was provided by description of the crystal structure of the ${\beta}2$-adrenoceptor-Gs complex in 2011. This review focused on recent findings in the conformational dynamics of G proteins and GPCRs during activation processes.

• Molecules and Cells
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• v.38 no.2
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• pp.105-111
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• 2015

The beta2-adrenergic receptor (${\beta}2AR$) belongs to the G protein coupled receptor (GPCR) family, which is the largest family of cell surface receptors in humans. Extra attention has been focused on the human GPCRs because they have been studied as important protein targets for pharmaceutical drug development. In fact, approximately 40% of marketed drugs directly work on GPCRs. GPCRs respond to various extracellular stimuli, such as sensory signals, neurotransmitters, chemokines, and hormones, to induce structural changes at the cytoplasmic surface, activating downstream signaling pathways, primarily through interactions with heterotrimeric G proteins or through G-protein independent pathways, such as arrestin. Most GPCRs, except for rhodhopsin, which contains covalently linked 11 cis-retinal, bind to diffusible ligands, having various conformational states between inactive and active structures. The first human GPCR structure was determined using an inverse agonist bound ${\beta}2AR$ in 2007 and since then, more than 20 distinct GPCR structures have been solved. However, most GPCR structures were solved as inactive forms, and an agonist bound fully active structure is still hard to obtain. In a structural point of view, ${\beta}2AR$ is relatively well studied since its fully active structure as a complex with G protein as well as several inactive structures are available. The structural comparison of inactive and active states gives an important clue in understanding the activation mechanism of ${\beta}2AR$. In this review, structural features of inactive and active states of ${\beta}2AR$, the interaction of ${\beta}2AR$ with heterotrimeric G protein, and the comparison with ${\beta}1AR$ will be discussed.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2000.04a
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• pp.17-19
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• 2000

Heterotrimeric G Proteins transduce ligand binding to a wide variety of seven transmembrane cell surface receptors into intracellular signals. The currently accepted model for the activation of G protein suggests that ligand-activated receptor accelerates GDP-GTP exchange reactions on the ${\alpha}$ subunit of the heterotrimeric G protein. At least seventeen distinct isoforms of the G${\alpha}$ subunit protein have been identified in mammalian organisms. Among them, the G${\alpha}$q family consists of five members whose ${\alpha}$ subunits show different expression patterns. G${\alpha}$q and G${\alpha}$11 seem to be almost ubiquitously expressed, whereas G${\alpha}$14 is predominantly expressed in spleen, lung, kidney and testis. G${\alpha}$16 and its murine counterpart G${\alpha}$15 are expressed in hematopoietic cells and has been shown to couple a wide variety of receptors to phosphoinositide-specific phospholipase C activity. Beta-isoforms of phospholipase C were shown to be activated by all members of G${\alpha}$q family, i.e., G${\alpha}$q, G${\alpha}$11, G${\alpha}$l4 and G${\alpha}$16 subunits either in reconstitution system. or in experiments using cDNA transfection with intact Cos-7 cells.

• Biomedical Science Letters
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• v.12 no.4
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• pp.405-411
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• 2006

Heterotrimeric GTP binding proteins (G proteins) mediate signal transduction generated by neurotransmitter and hormones. Among G-proteins, Go is classified as a member of the Go/Gi family and the most abundant heterotrimeric G protein in brain. Most of the mechanistic analyses on the activation of Go indicated its action to be mediated by the $G{\beta}{\gamma}$ dimer because downstream effectors for its ${\alpha}$ subunit have not been clearly defined. To determine the downstream effectors of alpha subunits of Go ($Go{\alpha}$), we used yeast two-hybrid system to screen $Go{\alpha}$ interacting partners in cDNA library from the human brain. A brain specific high mobility group box containing protein (BHX), A possible transcription factor, was identified as a $Go{\alpha}$ interacting protein. We confirmed interaction between $Go{\alpha}$ and BHX employing in vitro affinity binding assay. Moreover, active form of $Go{\alpha}$ preferentially interacts with BHX than inactive farm. Our findings indicate that $Go{\alpha}$ could modulate gene expression via interaction with BHX during neuronal or brain development.

• Toxicological Research
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• v.29 no.3
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• pp.149-155
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• 2013

G protein-coupled receptors (GPCRs) are membrane receptors; approximately 40% of drugs on the market target GPCRs. A precise understanding of the activation mechanism of GPCRs would facilitate the development of more effective and less toxic drugs. Heterotrimeric G proteins are important molecular switches in GPCR-mediated signal transduction. An agonist-activated receptor interacts with specific sites on G proteins and promotes the release of GDP from the $G{\alpha}$ subunit. Because of the important biological role of the GPCR-G protein coupling, conformational changes in the G protein upon receptor coupling have been of great interest. One of the most important questions was the interface between the GPCR and G proteins and the structural mechanism of GPCR-induced G protein activation. A number of biochemical and biophysical studies have been performed since the late 80s to address these questions; there was a significant breakthrough in 2011 when the crystal structure of a GPCR-G protein complex was solved. This review discusses the structural aspects of GPCR-G protein coupling by comparing the results of previous biochemical and biophysical studies to the GPCR-G protein crystal structure.

• The Korean Journal of Pain
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• v.19 no.1
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• pp.8-16
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• 2006

The regulators of the G protein signaling (RGS) proteins are responsible for the rapid acceleration of the GTPase-activity intrinsic to the heterotrimeric G protein alpha subunits. As GTPase-activating proteins (GAP), the RGS proteins negatively regulate the G-protein signals. Recently, the RGS proteins are known to be one of the important regulators of opioid signal transduction and the development of tolerance. The aim of this study was to review the recent discovery and understanding of the role of RGS proteins in opioid signaling and the development of tolerance. This information will be useful for medical personnel, particularly those involved in anesthesia and pain medicine, by helping them improve the effective use of opioids and develop new drugs that can prevent opioid tolerance.

• BMB Reports
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• v.41 no.9
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• pp.645-650
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• 2008

Nucleoside diphosphate kinase (NDPK) is involved in multiple signaling pathways in mammalian systems, including G-protein signaling. Arabidopsis NDPK2, like its mammalian counterparts, is multifunctional despite its initial discovery phytochrome-interacting protein. This similarity raises the possibility that NDPK2 may play a role in G-protein signaling in plants. In the present study, we explore the potential relationship between NDPK2 and the small G proteins, Pra2 and Pra3, as well as the heterotrimeric G protein, GPA1. We report a physical interaction between NDPK2 and these small G proteins, and demonstrate that NDPK2 can stimulate their GTPase activities. Our results suggest that NDPK2 acts as a GTPase-activating protein for small G proteins in plants. We propose that NDPK2 might be a missing link between the phytochrome-mediated light signaling and G protein-mediated signaling.