Cyclase

About: Cyclase is a research topic. Over the lifetime, 10162 publications have been published within this topic receiving 388566 citations.

Decreased stimulatory guanosine triphosphate binding protein in dogs with pressure-overload left ventricular failure.

Abstract: Alterations in the level and function of the stimulatory guanyl nucleotide binding protein (Gs) from the cardiac sarcolemma were examined in a canine model of heart failure. The present study is based on our previous investigations that demonstrated both a loss of beta-adrenergic agonist high-affinity binding sites and a decreased adenylate cyclase activity in sarcolemma from failing hearts. Using cholera toxin and [32P]NAD, we labeled the alpha subunit of Gs (Gs alpha) and found a 59% reduction in the level of this protein. Further, a 50% reduction in Gs activity was noted in a reconstitution assay utilizing membranes from the mouse S49 lymphoma cell line cyc-, which is deficient in Gs. These data suggest that, in this model of pressure-overload left ventricular failure, the acquired defect in the beta-adrenergic receptor/adenylate cyclase system involves a deficiency in the coupling protein Gs. Such an abnormality may explain the decreased adrenergic responsiveness of the failing left ventricle.

A conserved proline-rich region of the Saccharomyces cerevisiae cyclase-associated protein binds SH3 domains and modulates cytoskeletal localization.

Abstract: Saccharomyces cerevisiae cyclase-associated protein (CAP or Srv2p) is multifunctional. The N-terminal third of CAP binds to adenylyl cyclase and has been implicated in adenylyl cyclase activation in vivo. The widely conserved C-terminal domain of CAP binds to monomeric actin and serves an important cytoskeletal regulatory function in vivo. In addition, all CAP homologs contain a centrally located proline-rich region which has no previously identified function. Recently, SH3 (Src homology 3) domains were shown to bind to proline-rich regions of proteins. Here we report that the proline-rich region of CAP is recognized by the SH3 domains of several proteins, including the yeast actin-associated protein Abp1p. Immunolocalization experiments demonstrate that CAP colocalizes with cortical actin-containing structures in vivo and that a region of CAP containing the SH3 domain binding site is required for this localization. We also demonstrate that the SH3 domain of yeast Abp1p and that of the yeast RAS protein guanine nucleotide exchange factor Cdc25p complex with adenylyl cyclase in vitro. Interestingly, the binding of the Cdc25p SH3 domain is not mediated by CAP and therefore may involve direct binding to adenylyl cyclase or to an unidentified protein which complexes with adenylyl cyclase. We also found that CAP homologous from Schizosaccharomyces pombe and humans bind SH3 domains. The human protein binds most strongly to the SH3 domain from the abl proto-oncogene. These observations identify CAP as an SH3 domain-binding protein and suggest that CAP mediates interactions between SH3 domain proteins and monomeric actin.

Pharmacology and inotropic potential of forskolin in the human heart.

Abstract: We evaluated the effects of the diterpene compound forskolin in human myocardial adenylate cyclase preparations, isolated trabeculae and papillary muscles derived from failing human hearts, and acutely instrumented dogs Forskolin was a potent, powerful activator of human myocardial adenylate cyclase and produced maximal effects that were 482 (normally functioning left ventricle) and 613 (failing left ventricle) fold greater than isoproterenol In contrast to isoproterenol, forskolin retained full activity in membrane preparations derived from failing hearts In cyclase preparations, forskolin demonstrated unique substrate and Mg2+ kinetic properties that could be distinguished from hormone receptor-coupled agonists or fluoride ion The adenylate cyclase stimulatory effect of forskolin was synergistic with isoproterenol, apparently due to the location of forskolin activation being beyond the level of hormone receptor-agonist in the receptor-cyclase complex Forskolin was a potent positive inotrope in failing human myocardium, producing a stimulation of contraction that was similar to isoproterenol Finally, in open chest dogs forskolin was a positive inotropic agent that reduced preload and afterload We conclude that forskolin belongs to a class of agents that may have therapeutic potential in the treatment of congestive heart failure

The transmembrane glycoprotein CD38 is a catalytically active transporter responsible for generation and influx of the second messenger cyclic ADP-ribose across membranes

Abstract: CD38 is a type II transmembrane glycoprotein expressed in many vertebrate cells. It is a bifunctional ectoenzyme that catalyzes both the synthesis of Cyclic ADP-ribose (cADPR) from NAD+ and the degradation of cADPR to ADP-ribose by means of its ADP-ribosyl cyclase and cADPR-hydrolase activities, respectively. The cyclase also converts NGD+ to cyclic GDP-ribose (cGDPR), which is refractory to cADPR-hydrolase. cADPR, but not cGDPR, is a potent calcium mobilizer from intracellular stores. It has been demonstrated to be a new second messenger involved in the regulation of calcium homeostasis in many cell types, from plants to mammals. The number of physiological processes shown to be regulated by cADPR is steadily increasing. A topological paradox exists because ectocellularly generated cADPR acts intracellularly. Here we demonstrate that the catalytic functioning of CD38 is accompanied by a cADPR (cGDPR) -transporting activity across natural and artificial membranes. In resealed membranes from CD38+ human er...

Delineation of muscarinic receptor domains conferring selectivity of coupling to guanine nucleotide-binding proteins and second messengers.

Abstract: The cloning and functional expression of five mammalian muscarinic acetylcholine receptor genes (m1-m5) has revealed that m1, m3, and m5 primarily couple to stimulation of phosphoinositide (PI) turnover, whereas m2 and m4 are strongly linked to inhibition of adenylate cyclase, albeit not exclusively. To identify the structural domains responsible for this functional specificity, cDNAs encoding chimeric m2/m3 receptors were constructed. The abilities of these receptors to mediate stimulation of PI hydrolysis and inhibition of prostaglandin E2-stimulated cAMP accumulation, as well as the pertussis toxin (PTX) sensitivity of these responses, were examined after stable expression in mouse A9 L cells. Substitution of the putative third cytoplasmic loop (i3) of m2 with the corresponding m3 sequence resulted in a chimeric receptor that, similar to m3, stimulated PI breakdown by a PTX-insensitive mechanism but did not inhibit adenylate cyclase. Conversely, a chimeric m3 receptor containing the i3 domain of m2 showed the same functional profile as m2 (i.e., inhibition of adenylate cyclase and weak stimulation of PI turnover by a PTX-sensitive mechanism), indicating that the i3 loop is sufficient to determine coupling selectivity. Similarly, exchange of a short N-terminal segment of i3 (16 or 17 amino acids) between m2 and m3 resulted in chimeric receptors that gained the ability to mediate the functional responses of the wild-type receptor from which the segment was derived, although with substantially reduced efficiency. However, the chimeric m2 receptor containing the 17-amino acid m3 sequence in the N-terminal portion of i3 retained its ability to inhibit adenylate cyclase. Carbachol binding studies involving the use of the GTP analog 59-guanylyl imidodiphosphate and PTX-pretreated cells generally correlated well with the functional findings. Our data indicate that the N-terminal portion of i3 is a sufficient but not the exclusive determinant of coupling selectivity displayed by the various muscarinic receptors.