The guanosine triphosphate-binding proteins (G proteins) found in a variety of tissues transduce signals generated by ligand binding to cell surface receptors into changes in intracellular metabolism. Amino acid sequences of peptides prepared by partial proteolysis of the alpha subunit of a bovine brain G protein and the alpha subunit of rod outer-segment transducin were determined. The two proteins show regions of sequence identity as well as regions of diversity. A portion of the amino-terminal peptide sequence of each protein is highly homologous with the corresponding region in the ras protein (a protooncogene product). These similarities suggest that G proteins and ras proteins may have analogous functions.

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The metabolism of coenzyme A and control of its synthesis are reviewed. Pantothenate kinase is an important rate-controlling enzyme in the synthetic pathway of all tissues studied and appears to catalyze the flux-generating reaction of the pathway in cardiac muscle. This enzyme is strongly inhibited by coenzyme A and all of its acyl esters. The cytosolic concentrations of coenzyme A and acetyl coenzyme A in both liver and heart are high enough to totally inhibit pantothenate kinase under all conditions. Free carnitine, but not acetyl carnitine, deinhibits the coenzyme A-inhibited enzyme. Carnitine alone does not increase enzyme activity. Thus changes in the acetyl carnitine-to-carnitine ratio that occur with nutritional states provides a mechanism for regulation of coenzyme A synthetic rates. Changes in the rate of coenzyme A synthesis in liver and heart occurs with fasting, refeeding, and diabetes and in heart muscle with hypertrophy. The pathway and regulation of coenzyme A degradation are not understood.

The G protein ␤␥-dimer is required for receptor interaction and effector regulation. However, previous approaches have not identified the physiologic roles of individual subtypes in these processes. We used a gene knockout approach to demonstrate a unique role for the G protein ␥ 7 -subunit in mice. Notably, deletion of Gng7 caused behavioral changes that were associated with reductions in the ␣ olf -subunit content and adenylyl cyclase activity of the striatum. These data demonstrate that an individual ␥-subunit contributes to the specificity of a given signaling pathway and controls the formation or stability of a particular G protein heterotrimer.The heterotrimeric G proteins control diverse biological processes by conveying signals from cell-surface receptors to intracellular effectors. Although function was originally ascribed to the GTP-bound ␣-subunit, it is now well established that the ␤␥-dimer plays active roles in the signaling process through upstream recognition of receptors and downstream regulation of effectors (1). Molecular cloning has identified at least 5 ␤-and 12 ␥-subunit genes in the mouse and human genomes. Structurally, ␥-subunits are the most diverse, with four subgroups that show less than 50% identity to each other (2). Moreover, ␥-subunits exhibit very different temporal (3, 4) and spatial (5) patterns of expression. These characteristics suggest that ␥-subunits have heterogeneous functions. However, comparison of their biochemical properties has revealed only modest differences (6 -8), perhaps because of the inherent limitations of transfection and reconstitution approaches. Gene ablation in mice has proven to be a powerful approach to identifying the functional roles of several G protein ␣-subunits (9). We report the first use of a gene targeting strategy to identify a unique function for a member of the ␥-subunit family.The G protein ␥ 7 -subunit (G␥ 7 ) was originally cloned from bovine brain (10). In situ hybridization of rat brain sections revealed that mRNA for G␥ 7 is most highly expressed in the striatum (5), where it is found in 40 -50% of medium sized neurons in the caudate putamen (11). The regional expression of mRNA for G␥ 7 in the brain mirrors that of the striatumenriched D 1 dopamine receptor (D1R), 1 G␣ olf , and adenylyl cyclase Type V (12), suggesting involvement of G␥ 7 in the G␣ olf -mediated stimulation of adenylyl cyclase by dopamine. Single cell RT-PCR analysis confirms that D1R and G␥ 7 are expressed in the same subset of rat neurons (13). Ribozyme suppression studies support a role for G␥ 7 in the endogenous ␤-adrenergic receptor pathway (14) and the heterologously expressed D1R pathway in human embryonic kidney cells (13).

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The G protein-coupled receptor (GPCR) kinases (GRKs) phosphorylate and desensitize agonistoccupied GPCRs. GRK2-mediated receptor phosphorylation is preceded by the agonist-dependent membrane association of this enzyme. Previous in vitro studies with purified proteins have suggested that this translocation may be mediated by the recruitment of GRK2 to the plasma membrane by its interaction with the free ␤␥ subunits of heterotrimeric G proteins (G␤␥). Here we demonstrate that this mechanism operates in intact cells and that specificity is imparted by the selective interaction of discrete pools of G␤␥ with receptors and GRKs. Treatment of Cos-7 cells transiently overexpressing GRK2 with a ␤-receptor agonist promotes a 3-fold increase in plasma membrane-associated GRK2. This translocation of GRK2 is inhibited by the carboxyl terminus of GRK2, a known G␤␥ sequestrant. Furthermore, in cells overexpressing both GRK2 and G␤ 1 ␥ 2 , activation of lysophosphatidic acid receptors leads to the rapid and transient formation of a GRK͞G␤␥ complex. That G␤␥ specificity exists at the level of the GPCR and the GRK is indicated by the observation that a GRK2͞G␤␥ complex is formed after agonist occupancy of the lysophosphatidic acid and ␤-adrenergic but not thrombin receptors. In contrast to GRK2, GRK3 forms a G␤␥ complex after stimulation of all three GPCRs. This G␤␥ binding specificity of the GRKs is also ref lected at the level of the purified proteins. Thus the GRK2 carboxyl terminus binds G␤ 1 and G␤ 2 but not G␤ 3 , while the GRK3 fusion protein binds all three G␤ isoforms. This study provides a direct demonstration of a role for G␤␥ in mediating the agonist-stimulated translocation of GRK2 and GRK3 in an intact cellular system and demonstrates isoform specificity in the interaction of these components.Exposure of G protein-coupled receptors (GPCRs) to an agonist often results in rapid attenuation of receptor responsiveness, a process termed desensitization. Uncoupling of the receptor from its cognate heterotrimeric G protein underlies the rapid phase of this process and is mediated, at least in part, by receptor phosphorylation (reviewed in ref. 1). Two distinct classes of serine͞threonine kinases phosphorylate GPCRs; the second messenger-dependent protein kinases (cAMPdependent protein kinase and protein kinase C) and the second messenger-independent GPCR kinases (GRKs). On the basis of structural and functional similarities, the six known members of the GRK family have been divided into three subfamilies: (i) rhodopsin kinase (GRK1), (ii) the ␤-adrenergic receptor (␤AR) kinase subfamily (GRK2 and GRK3), and (iii) The GRK4 subfamily (GRK4, GRK5, and GRK6) (reviewed refs. 2 and 3).The members of the ␤AR kinase subfamily of GRKs (GRK2 and GRK3) exhibit an agonist-dependent association with the plasma membrane in cellular systems (4). Thus treatment of DDT 1 MF-2 or S49 cells with a ␤-agonist leads to a rapid translocation of GRK2 activity from the cytosol to the plasma membrane (4). Agonist-induced GRK2 translocation ...

With the growing awareness that the G protein ␤ and ␥ subunits directly regulate the activities of various enzymes and ion channels, the importance of identifying and characterizing these subunits is underscored. In this paper, we report the isolation of cDNA clones encoding eight different human ␥ subunits, including three novel forms designated ␥ 4 , ␥ 10 , and ␥ 11 . The predicted protein sequence of ␥ 4 shares the most identity (60 -77%) with ␥ 2 , ␥ 3 , and ␥ 7 and the least identity (38%) with ␥ 1 . The ␥ 4 is modified by a geranylgeranyl group and is capable of interacting with both ␤ 1 and ␤ 2 but not with ␤ 3 . The predicted protein sequence of ␥ 10 shows only modest to low identity (35-53%) with the other known ␥ subunits, with most of the differences concentrated in the N-terminal region, suggesting ␥ 10 may interact with a unique subclass of ␣. The ␥ 10 is modified by a geranylgeranyl group and is capable of interacting with ␤ 1 and ␤ 2 but not with ␤ 3 . Finally, the predicted protein sequence of ␥ 11 shows the most identity to ␥ 1 (76% identity) and the least identity to the other known ␥ (33-44%). Unlike most of the other known ␥ subunits, ␥ 11 is modified by a farnesyl group and is not capable of interacting with ␤ 2 . The close resemblance of ␥ 11 to ␥ 1 raises intriguing questions regarding its function since the mRNA for ␥ 11 is abundantly expressed in all tissues tested except for brain, whereas the mRNA for ␥ 1 is expressed only in the retina where the protein functions in phototransduction.Intracellular transmission of extracellular signals are most commonly mediated by a family of guanine nucleotide-binding proteins (G proteins) that couple with various receptors and effectors to produce appropriate cellular responses. The G proteins are heterotrimers, composed of ␣, ␤, and ␥ subunits. In response to binding of the appropriate ligand, the receptor stimulates the exchange of bound GDP for GTP on the ␣ subunit, resulting in the dissociation of the ␣ subunit from the ␤ and ␥ subunits. The GTP-bound ␣ subunit has been shown to directly regulate the activity of downstream effectors (1-3). Recently, it has been shown that the ␤␥ subunits, which exist as a tightly associated complex in vivo (1), can also regulate the activity of a specific subset of downstream effectors, including adenylyl cyclase subtypes II and IV, phospholipase A2, phospholipase C subtypes ␤1, 2, and 3, and K ϩ and Ca 2ϩ channels (4 -6). Thus, the G protein ␣ and ␤␥ subunits produce bifurcating signals that regulate effector function. Moreover, the ␤␥ subunits can directly bind to receptors (7) and can increase agonist-dependent phosphorylation and desensitization of receptors by directly interacting and recruiting the ␤-adrenergic receptor kinases to the membrane (8 -9). Thus, the ␤␥ subunits play prominent roles in both effector regulation and receptor recognition. As the number of ␣, ␤, and ␥ subunits continues to grow, the task of unraveling the subunit composition and function of individual G proteins is becoming more com...

Although the development and increasingly widespread availability of effective and safe vaccines provides the greatest hope for the future recovery from the increasingly devastating COVID-19 pandemic, there are other preventive efforts that offer an immediate route to decreasing morbidity and mortality. Genomic surveillance is emerging as a vital necessity to achieve effective mitigation and containment. Since SARS-CoV-2 variants have already been detected, it is crucial to obtain reliable evidence about whether they are more contagious, virulent, or more resistant to the available COVID-19 vaccines well before they spread throughout the world. Genomic surveillance leverages applications of next-generation sequencing, creates the availability of whole genome data, and advances phylogenetic methods. These methods offer novel means to detect variants that are phenotypically or antigenically different. Genomic surveillance will facilitate greater early anticipation as well as initiation of effective strategies to mitigate and contain outbreaks of SARS-CoV-2 variants and other novel viruses.