Cyclase

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

Agonist-promoted coupling of the beta-adrenergic receptor with the guanine nucleotide regulatory protein of the adenylate cyclase system.

Abstract: Binding of the beta-adrenergic agonist [3H]hydroxybenzylisoproterenol to the beta-adrenergic receptor of rat reticulocyte membranes results in the coupling of the receptor to the guanine nucleotide regulatory protein associated with the adenylate cyclase system. This regulatory component, referred to as the G-protein, was identified by its specific [32P]-ADP-ribosylation catalyzed by cholera toxin. Incubation of [32P]ADP-ribosylated rat reticulocyte membranes with the [3H]hydroxybenzylisoproterenol agonist prior to membrane solubilization and gel exclusion chromatography resulted in the coelution of the 42,000 Mr [32P]ADP-ribosylated G-proteins with the agonist-occupied beta-adrenergic receptors. The receptor-G-protein complex was not formed when receptors were unoccupied or occupied with antagonists at the time of solubilization. Incubation of rat reticulocyte membranes with [3H]hydroxybenzylisoproterenol in the presence of guanine nucleotides reversed or prevented the formation of this receptor-G-protein complex. These data provide direct evidence for the molecular interactions promoted by agonist occupancy of beta-adrenergic receptors. It is probable that the formation of a receptor-G-protein complex is crucial for catecholamine stimulation of the adenylate cyclase enzyme and, hence, transmembrane information transfer.

Two amino acid substitutions convert a guanylyl cyclase, RetGC-1, into an adenylyl cyclase

Abstract: Guanylyl cyclases (GCs) and adenylyl cyclases (ACs) have fundamental roles in a wide range of cellular processes. Whereas GCs use GTP as a substrate to form cGMP, ACs catalyze the analogous conversion of ATP to cAMP. Previously, a model based on the structure of adenylate cyclase was used to predict the structure of the nucleotide-binding pocket of a membrane guanylyl cyclase, RetGC-1. Based on this model, we replaced specific amino acids in the guanine-binding pocket of GC with their counterparts from AC. A change of two amino acids, E925K together with C995D, is sufficient to completely alter the nucleotide specificity from GTP to ATP. These experiments strongly validate the AC-derived RetGC-1 structural model and functionally confirm the role of these residues in nucleotide discrimination.

Abolition of the expression of inhibitory guanine nucleotide regulatory protein Gi activity in diabetes.

Abstract: Many cell-surface receptors for hormones appear to exert their effects on target cells by interacting with specific guanine nucleotide binding regulatory proteins (G-proteins) which couple receptors to their second-messenger signal generation systems. A common intracellular second messenger, which is used by many hormones, is cyclic AMP. This is produced by adenylate cyclase, whose activity is controlled by two G-proteins, Gs which mediates stimulatory effects and Gi inhibitory effects on adenylate cyclase activity1. In liver, the hormone glucagon increases intracellular cAMP concentrations by activating adenylate cyclase by a Gs-mediated process. This effect of glucagon is antagonised by the hormone insulin, although the molecular mechanism by which insulin elicits its actions is obscure. However, insulin receptors exhibit a tyrosyl kinase activity2 and appear to interact with G-proteins2,3, perhaps by causing phosphorylation of them4. In type I diabetes, circulating insulin levels are abnormally low, giving rise to gross perturbations of metabolism as well as to a variety of complications such as ionic disturbances, neuropathies of the nervous system, respiratory and cardiovascular aberrations and predispostion to infection5. We show here that experimentally-induced type I diabetes leads to the loss of expression of G{ in rat liver. As it has been suggested that Gi may couple receptors to K+-channels6,7 as well as mediating the inhibition of adenylate cyclase, aberrations in the control of expression of this key regulatory protein in type I diabetes may be expected to lead to pleiotropic effects.

Identification and functional analysis of genes controlling biosynthesis of 2-methylisoborneol

Abstract: To identify the genes for biosynthesis of the off-flavor terpenoid alcohol, 2-methylisoborneol (2-MIB), the key genes encoding monoterpene cyclase were located in bacterial genome databases by using a combination of hidden Markov models, protein–family search, and the sequence alignment of their gene products. Predicted terpene cyclases were classified into three groups: sesquiterpene, diterpene, and other terpene cyclases. Genes of the terpene cyclase group that form an operon with a gene encoding S-adenosyl-l-methionine (SAM)-dependent methyltransferase were found in genome data of seven microorganisms belonging to actinomycetes, Streptomyces ambofaciens ISP5053, Streptomyces coelicolor A3(2), Streptomyces griseus IFO13350, Streptomyces lasaliensis NRRL3382R, Streptomyces scabies 87.22, Saccharopolyspora erythraea NRRL2338, and Micromonospora olivasterospora KY11048. Among six microorganisms tested, S. ambofaciens, S. coelicolor A3(2), S. griseus, and S. lasaliensis produced 2-MIB but M. olivasterospora produced 2-methylenebornane (2-MB) instead. The regions containing monoterpene cyclase and methyltransferase genes were amplified by PCR from S. ambofaciens, S. lasaliensis, and Saccharopolyspora erythraea, respectively, and their genes were heterologously expressed in Streptomyces avermitilis, which was naturally deficient of 2-MIB biosynthesis by insertion and deletion. All exoconjugants of S. avermitilis produced 2-MIB. Full-length recombinant proteins, monoterpene cyclase and methyltransferase of S. lasaliensis were expressed at high level in Escherichia coli. The recombinant methyltransferase catalyzed methylation at the C2 position of geranyl diphosphate (GPP) in the presence of SAM. 2-MIB was generated by incubation with GPP, SAM, recombinant methyltransferase, and terpene cyclase. We concluded that the biosynthetic pathway involves the methylation of GPP by GPP methyltransferase and its subsequent cyclization by monoterpene cyclase to 2-MIB.