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PubMed1990

Effect of calcium and beta-adrenoceptor antagonists on beta-adrenoceptor density and Gs alpha expression in human atria.

In 21 patients undergoing open heart surgery the effects of the beta-adrenoceptor antagonists propranolol and sotalol and the calcium antagonist nifedipine (alone or in combination) on right atrial beta-adrenoceptor density and G protein expression were studied. The non-selective beta-adrenoceptor antagonists increased both right atrial beta 1- and beta 2-adrenoceptor density; this increase was not affected by nifedipine. There was no correlation between beta-adrenoceptor density and expression of the G protein subunit Gs alpha suggesting independent regulation of the gene expression for G proteins and their coupled receptors.

Adrenergic beta-Antagonists↗

PubMed1994

Catabolite modification of acid tolerance of Streptococcus mutans GS-5.

The acid tolerance of Streptococcus mutans GS-5 in standard pH-drop assays was found to be affected by the sugar used in the assay and also by the sugar used for growth of the organism. For example, acid tolerance was lower when galactose was used as catabolite than when glucose was used, apparently because galactose/proton symport brought protons extruded by the F-ATPase back into the cell and thus reduced delta pH across the cell membrane. The acid tolerance of glycolysis was related directly to the capacities of the cells to produce acid glycolytically, or probably more correctly, to their capacities to produce adenosine triphosphate but not to acid tolerance of phosphotransferase systems for sugar uptake. Thus, glycolytic acid tolerance of S. mutans depends not only on environmental factors such as potassium or magnesium levels but also on the specific catabolites the organism is metabolizing or to which it has become metabolically adapted.

Adaptation, Physiological↗

PubMed1988

Opiate-inhibited adenylate cyclase in rat brain membranes depleted of Gs-stimulated adenylate cyclase.

Opiate agonists inhibit adenylate cyclase in brain membranes, but under normal conditions the maximal inhibition is small (10-15%). When rat brain membranes were preincubated at pH 4.5, washed, and then assayed for adenylate cyclase at pH 7.4, stimulation of activity by agents (fluoride, guanylyl-5'-imidodiphosphate, cholera toxin) that act through the stimulatory GTP-binding coupling protein (Gs) protein was lost. At the same time, inhibition of basal adenylate cyclase by opiate agonists was increased to a maximum of 30-40%. Opiate inhibition was maximal at low magnesium concentrations (less than 5 mM), required guanine nucleotides, and decreased the Vmax, not Km, of the enzyme. Incubation of membranes with pertussis toxin lowered the apparent affinity for agonists in inhibiting activity. The delta opioid agonists were more potent than mu agonists, and the Ke values for naloxone in blocking agonist inhibition were similar for both mu and delta agonists (50-90 nM). These results suggest that inhibition of adenylate cyclase in brain is not mediated by mu opiate receptors, but whether classic high-affinity delta and kappa receptors are involved with this enzyme cannot be confirmed by these experiments.

Adenylate Cyclase Toxin↗

PubMed1996

Irreversible paraben inhibition of glycolysis by Streptococcus mutans GS-5.

Parabens were found to inhibit irreversibly glycolysis by the cariogenic dental plaque bacterium Streptococcus mutans GS-5 and to decrease the capacity of the bacterium to lower the pH in dense cell suspensions containing excess glucose. The hierarchy of effectiveness was butyl > propyl > ethyl > methyl paraben. Results of studies of the nature of glycolytic inhibition by butyl paraben indicated that it could act at millimolar concentrations as an irreversible inhibitor of the phosphotransferase system for sugar uptake and was lethal for the bacterium at these same levels. Butyl paraben acted also as a reversible inhibitor of the F-ATPase of the organism. Overall, it appeared that the lethal actions of parabens can be interpreted at least in part as due to irreversible damage to key enzymes, such as those of the phosphotransferase system.

Food Preservatives↗

PubMed1987

Prostacyclin analogues reduce ADP-ribosylation of the alpha-subunit of the regulatory Gs-protein and diminish adenosine (A2) responsiveness of platelets.

Prostacyclin and adenosine activate adenylate cyclase in human platelet membranes and inhibit platelet aggregation. Results are presented which show that prolonged incubation of platelets with iloprost (a stable prostacyclin analogue) results in a reduction in the capacity for adenylate cyclase activation by the adenosine analogue 5'-(N-ethyl)-carboxamidoadenosine (NECA), NaF, guanyl-5'-yl imidodiphosphate or GTP. However, iloprost pretreatment resulted in no change in the binding of [3H]-NECA to platelet membranes. These results contrast with those obtained after pretreatment with 2-chloroadenosine which revealed no change in NaF or guanyl-5'-yl imidodiphosphate sensitivity of adenylate cyclase. Pretreatment with 2-chloroadenosine resulted in reduced NECA-dependent adenylate cyclase activation, and loss of [3H]-NECA binding sites. The heterologous desensitization of adenosine A2-receptors by iloprost is accompanied by a loss (greater than 80%) of a 45 kDa protein from the plasma membrane, as revealed by [32P]-ADP-ribosylation in the presence of cholera toxin. It is proposed that this example of heterologous desensitization is mediated by elimination of Gs alpha, a subunit of the stimulatory guanyl nucleotide-binding regulatory protein.

2-Chloroadenosine↗

PubMed2026

Seed-type vacuolar processing enzymes recognize the 619th asparagine residue to posttranslationally cleave the HMW-GS 1Dy10-m619SN allele.

High molecular weight glutenin subunits (HMW-GSs) are critical grain storage proteins in wheat, which govern its unique processing quality. A HMW-GS 1Dy10 allele variant (1Dy10-m619SN), carrying a serine-to-asparagine substitution at the 619th residue, undergoes partial posttranslational cleavage. This modification leads to improved cookie-making quality. However, the enzymes mediating this cleavage remain unknown. In this study, we identified vacuolar processing enzymes (VPEs) as candidates for 1Dy10-m619SN processing using TurboID-based proximity labeling and RNA-seq analysis. In vitro cleavage assays confirmed that VPEs catalyzed 1Dy10-m619SN cleavage. Phylogenic analysis revealed that there are two seed-type VPEs in wheat, TaVPEI and TaVPEII, with TaVPEI being further subdivided into TaVPEI-1, TaVPEI-2, and TaVPEI-3. Despite sharing conserved catalytic domains, these isoforms display distinct temporal expression patterns, with TaVPEI-1 expression showing the strongest correlation with the posttranslational cleavage of 1Dy10-m619SN. TaVPEI-1 protein is localized to the vacuole, the well-known deposition site for HMW-GSs. Overexpression of TaVPEI-1 in wheat enhances the 1Dy10-m619SN cleavage. Collectively, these findings demonstrate that the seed-type VPEs in wheat are responsible for the posttranslational cleavage of 1Dy10-m619SN, which provides new insights into the molecular basis of wheat's unique processing quality.

Triticum↗

PubMed1997

The stability of the agonist beta2-adrenergic receptor-Gs complex: evidence for agonist-specific states.

A restricted version of the ternary complex model for receptor-G protein complex formation has recently been proposed. Known as the two-state model, this model proposes that in the context of agonist and G protein interactions, only two thermodynamic states exist for the receptor: active (R*) and inactive (R). One form of this model suggests that only the R* state of the receptor is capable of interacting with and subsequently activating G proteins. We directly tested the kinetic aspects of a strict two-state receptor model in a cell line containing the native beta2-adrenergic receptor that is capable of inducing Gs expression. We examined adenylyl cyclase activity in the presence of limiting GTP levels and concluded that there exists a different rate of heterotrimer dissociation (i.e., HR*G yields HR* + G*) for different beta2-agonists. This finding is inconsistent with a strict two-state model in which R* is a characteristic of the receptor that is independent of the identity of the agonist. It implies that agonist activation of adenylyl cyclase is more complicated than a simple two-state model.

Adenylyl Cyclases↗

PubMed2004

The Gs-linked receptor GPR3 maintains meiotic arrest in mammalian oocytes.

Mammalian oocytes are held in prophase arrest by an unknown signal from the surrounding somatic cells. Here we show that the orphan Gs-linked receptor GPR3, which is localized in the oocyte, maintains this arrest. Oocytes from Gpr3 knockout mice resume meiosis within antral follicles, independently of an increase in luteinizing hormone, and this phenotype can be reversed by injection of Gpr3 RNA into the oocytes. Thus, the GPR3 receptor is a link in communication between the somatic cells and oocyte of the ovarian follicle and is crucial for the regulation of meiosis.

Adenylyl Cyclases↗

PubMed1990

Control of yeast mating signal transduction by a mammalian beta 2-adrenergic receptor and Gs alpha subunit.

To facilitate functional and mechanistic studies of receptor-G protein interactions, [corrected] the human beta 2-adrenergic receptor (h beta-AR) has been expressed in Saccharomyces cerevisiae. This was achieved by placing a modified h beta-AR gene under control of the galactose-inducible GAL1 promoter. After induction by galactose, functional h beta-AR was expressed at a concentration several hundred times as great as that found in any human tissue. As determined from competitive ligand binding experiments, h beta-AR expressed in yeast displayed characteristic affinities, specificity, and stereoselectivity. Partial activation of the yeast pheromone response pathway by beta-adrenergic receptor agonists was achieved in cells coexpressing h beta-AR and a mammalian G protein (Gs) alpha subunit-demonstrating that these components can couple to each other and to downstream effectors when expressed in yeast. This in vivo reconstitution system provides a new approach for examining ligand binding and G protein coupling to cell surface receptors.

Amino Acid Sequence↗

PubMed1988

Carboxyl terminal domain of Gs alpha specifies coupling of receptors to stimulation of adenylyl cyclase.

The alpha subunits of Gs and Gi link different sets of hormone receptors to stimulation and inhibition, respectively, of adenylyl cyclase. A chimeric alpha i/alpha s cDNA was constructed that encodes a polypeptide composed of the amino terminal 60% of an alpha i chain and the carboxyl terminal 40% of alpha s. The cDNA was introduced via a retroviral vector into S49 cyc- cells, which lack endogenous alpha s. Although less than half of the hybrid alpha chain is derived from alpha s, its ability to mediate beta-adrenoceptor stimulation of adenylyl cyclase matched that of the normal alpha s polypeptide expressed from the same retroviral vector in cyc- cells. This result indicates that carboxyl terminal amino acid sequences of alpha s contain the structural features that are required for specificity of interactions with the effector enzyme, adenylyl cyclase, as well as with the hormone receptor.

Adenylyl Cyclases↗

PubMed1980

Mutational loss of sensitivity to mutacin GS-5 in Streptococcus pyogenes: characterization of a mutant deficient in receptor protein.

By means of a stepwise selection procedure, mutants capable of growing in the presence of relatively high multiplicities of a bacteriocin from Streptococcus mutans GS-5 were obtained from a sensitivie strain of Streptococcus pyogenes. Mutacin-neutralizing activity of cell extracts containing receptor protein was examined in one variant that adsorbed 1/6 the amount of bacteriocin adsorbed by the parent strain under conditions equivalent to "saturation." Partially purified receptor protein from both parent and mutant cells neutralized an equivalent amount of bacteriocin on a weight-to-weight basis, indicating that in vitro there was no significant difference in affinity for the mutacin between the respective receptor fractions. Cell extracts from the mutant, solubilized by treatment with trichloroacetic acid, neither neutralized mutacin activity nor interfered with receptor protein-mediated mutacin neutralization in vitro. The mutant phenotype may thus represent a cell surface density of receptor protein which results in the adsorption of sublethal amounts of mutacin. The mutant retained its sensitivity to other mutacins, e.g., those produced by strains LM-7 and BHT of S. mutans, and did not differ from wild-type cells with respect to either detergent sensitivity (sodium lauryl sulfate and Triton X-100) or to inhibition by penicillin, rifampin, bacitracin, erythromycin, and tetracycline.

Bacterial Proteins↗

PubMed1981

Mutational loss of susceptibility to mutacin GS-5 in Streptococcus pyogenes: surface protein in a tolerant variant.

A variant (S4340) nonsusceptible to mutacin GS-5 was previously obtained from a strain of Streptococcus pyogenes susceptible to this bacteriocin. The variant was found to adsorb as much bacteriocin as parent cells and exhibit similar susceptibility to seven antibiotics and two detergents. Electrophoretic analysis of protein dissociated from mutant cells by brief sonication revealed the presence of a 74,000-dalton polypeptide not discernible in profiles obtained from susceptible parent cells. The precise role of this tolerance-associated marker remains to be determined. The protein does not appear to be an exported product transiently associated with the cell envelope.

Anti-Bacterial Agents↗

PubMed1981

Enhanced transmembrane proton conductance in Streptococcus mutans GS-5 due to ionophores and fluoride.

The uptake of protons by intact cells of Streptococcus mutans GS-5 was measured directly by assessing the pH increase in lightly buffered cell suspensions as protons moved across the plasma membrane after acid pulses. The barrier function of the cell membrane for protons was disrupted completely by 5% (vol/vol) butanol. This function was compromised severely by the ionophores valinomycin and gramicidin and by the uncoupler carbonylcyanide-m-chlorophenyl hydrazone. Proton conduction across the membrane was also enhanced by fluoride. It appeared that HF traversed the membrane and acted as a carrier. Once in the relatively alkaline cytoplasm, HF dissociated to yield F- and H+, which acted to acidify the cytoplasm and reduced the pH difference across the membrane.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗

PubMed1991

Electron Transport in the Dissimilatory Iron Reducer, GS-15.

Mechanisms for electron transport to Fe(III) were investigated in GS-15, a novel anaerobic microorganism which can obtain energy for growth by coupling the complete oxidation of organic acids or aromatic compounds to the reduction of Fe(III) to Fe(II). The results indicate that Fe(III) reduction proceeds through a type b cytochrome and a membrane-bound Fe(III) reductase which is distinct from the nitrate reductase.

Journal Article↗

PubMed1999

Enhanced (+)-catechin transglucosylating activity of Streptococcus mutans GS-5 glucosyltransferase-D due to fructose removal.

The (+)-catechin transglucosylating activities of several glucosyltransferases (GTFs) from the genus Streptococcus were compared. For this purpose, a mixture of four GTFs from Streptococcus sobrinus SL-1 and recombinant GTF-B and GTF-D from Streptococcus mutans GS-5 expressed in Escherichia coli were studied. It was shown that after removal of alpha-glucosidase activity, GTF-D transglucosylated catechin with the highest efficiency. A maximal yield (expressed as the ratio of moles of glucoside formed to moles of catechin initially added) of 90% was observed with 10 mM catechin and 100 mM sucrose (K(m), 13 mM) in 125 mM potassium phosphate, pH 6.0, at 37 degrees C. (1)H and (13)C nuclear magnetic resonance spectroscopy revealed the structures of two catechin glucosides, (+)-catechin-4'-O-alpha-D-glucopyranoside and (+)-catechin-4',7-O-alpha-di-D-glucopyranoside. Fructose accumulation during glucosyl transfer from sucrose to the acceptor competitively inhibited catechin transglucosylation (K(i), 9.3 mM), whereas glucose did not inhibit catechin transglucosylation. The addition of yeasts was studied in order to minimize fructose inhibition by means of fructose removal. For this purpose, the yeasts Pichia pastoris and the mutant Saccharomyces cerevisiae T2-3D were selected because of their inabilities to utilize sucrose. Addition of P. pastoris or S. cerevisiae T2-3D to the standard reaction mixture resulted in a twofold increase in the duration of the maximum GTF-D transglucosylation rate. The addition of the yeasts also stimulated sucrose utilization by GTF-D.

Catechin↗

PubMed1988

Tn916 insertional inactivation of multiple genes on the chromosome of Streptococcus mutans GS-5.

Streptococcus mutans GS-5 was transformed with the Escherichia coli plasmid pAM150 containing the cloned streptococcal transposon Tn916. Southern blot analyses with the tetracycline-resistant determinant of Tn916 showed that Tn916 was inserted into the chromosome of S. mutans at a variety of different sites. Tn916 insertions resulted in the inactivation of genes that code for various steps in the biosynthesis of several different amino acids. Two auxotrophs which contained a single copy of Tn916 were shown to revert to prototrophy at frequencies of about 10(-8). All of the revertant prototrophs were susceptible to tetracycline, indicating regeneration of the functional gene by excision of Tn916.

DNA Transposable Elements↗

PubMed1990

Size of the Streptococcus mutans GS-5 chromosome as determined by pulsed-field gel electrophoresis.

Rare cutting restriction endonucleases were used to cut the Streptococcus mutans chromosome into large fragments. Restriction enzymes utilizing recognition sites containing 6-, 7-, or 8-base-pair sequences with only G and C nucleotides produced few fragments, most of which were greater than 100 kilobase pairs in size. Addition of the fragments from digests of SmaI, NotI, ApaI, RsrII, and EagI yielded a molecular size for the S. mutans GS-5 genome of 2,819 +/- 60 kilobase pairs.

Chromosomes, Bacterial↗

PubMed1990

Evidence that a low-affinity sucrose phosphotransferase activity in Streptococcus mutans GS-5 is a high-affinity trehalose uptake system.

High-affinity sucrose uptake in the oral pathogen Streptococcus mutans is mediated by the phosphoenolpyruvate-dependent phosphotransferase system. In this report, we provide evidence that a lower-affinity sucrose phosphotransferase system in S. mutans GS-5, previously described by others, is in fact a high-affinity trehalose uptake system that also recognizes sucrose as a substrate.

Biological Transport, Active↗