3',5'-cyclic nucleotide phosphodiesterase from human brain

3':5'-Cyclic nucleotide phosphodiesterase was isolated from human brain and characterized. After the first stage of purification on phenyl-Sepharose, the enzyme activity was stimulated by Ca2+ and micromolar concentrations of cGMP. High pressure liquid chromatography on a DEAE-TSK-3SW column permitted to identify three ranges of enzymatic activity designated as PDE I, PDE II and PDE III. Neither of the three enzymes possessed a high selectivity for cAMP and cGMP substrates. The catalytic activity of PDE I and PDE II increased in the presence of Ca2+-calmodulin (up to 6-fold); the degradation of cAMP was decreased by cGMP. The Ca2+-calmodulin stimulated PDE I and PDE II activity was decreased by W-7. PDE I and PDE II can thus be classified as Ca2+-calmodulin-dependent phosphodiesterases. With cAMP as substrate, the PDE III activity increased in the presence of micromolar concentrations of cGMP (up to 10-fold), Ca2+ and endogenous calmodulin (up to 2-3-fold). No additivity in the effects of saturating concentrations of these compounds on PDE III was observed. Ca2+ did not influence the rate of cGMP hydrolysis catalyzed by PDE III. In comparison with PDE I and PDE II, the inhibition of PDE III was observed at higher concentrations of W-7 and was not limited by the basal level of the enzyme. These results do not provide any evidence in favour of the existence of several forms of the enzyme in the PDE III fraction. The double regulation of PDE III creates some difficulties for its classification.     

Purification and characterization of a low-Km 3':5'-cyclic adenosine phosphodiesterase from post-meiotic male mouse germ cells.

We describe the purification and the study of the kinetic and hydrodynamic properties of a 'low Km' cAMP phosphodiesterase specifically expressed in haploid male germ cells of the mouse. The enzyme has been purified approx. 13,000-fold with respect to the activity in total cell homogenate. The purified enzyme hydrolyzed specifically cAMP with a Km of 3.3 microM and with a Vmax of 10.5 mumol of cAMP hydrolyzed/min per mg of protein. The hydrolytic activity was neither stimulated nor inhibited by cGMP, whereas it was inhibited by RO 20-1724 and Rolipram. The enzyme showed a Stokes radius of 3.8 nm and a sedimentation coefficient of 3.1 S, corresponding to a native molecular mass of 50 kDa and a frictional ratio of 1.53. Sodium dodecyl sulphate polyacrylamide gel electrophoresis analysis of sucrose gradient fractions of the purified enzyme showed a major band of 43 kDa copeaking with enzyme activity.     

Isolation and characterization of PDE10A, a novel human 3', 5'-cyclic nucleotide phosphodiesterase.

A gene encoding a novel human 3', 5'-cyclic nucleotide phosphodiesterase (PDE) was identified and characterized. PDE10A1 encodes a protein that is 779 amino acids in length. An incomplete cDNA for a second 5'-splice variant, PDE10A2, was isolated. The proteins encoded by the two variants share 766 amino acids in common. This common region includes an amino-terminal domain with partial homology to the cGMP-binding domains of PDE2, PDE5 and PDE6 as well as a carboxy-terminal region with homology to the catalytic regions of mammalian PDEs. Northern analysis revealed that PDE10A is widely expressed. The PDE10A gene was mapped to three yeast artificial chromosomes (YACs) that contain human DNA from chromosome 6q26-27. A recombinant protein corresponding to the 766 amino acid region common to PDE10A1 and PDE10A2 was expressed in yeast. It hydrolyzed both cAMP and cGMP. Inhibitors that are selective for other PDE families are poor inhibitors of PDE10A; however, PDE10A is inhibited by the non-specific PDE inhibitor, IBMX.     

Studies of the 2':3'-cyclic nucleotide phosphodiesterase of Haemophilus influenzae

The 2':3'-cyclic nucleotide phosphodiesterase:3'-nucleotidase of Haemophilus influenzae was purified from a periplasmic preparation by affinity chromatographic techniques. The enzyme-catalysed hydrolysis of 2':3'-cyclic AMP to adenosine without accumulation of the intermediate substrate 3'-AMP was demonstrated by high performance liquid chromatography. Competitive inhibition of the enzyme by a variety of nucleosides and mononucleotides indicated the presence of either purine or pyrimidine bases to be essential for selective interactions with the enzyme, and confirmed the need for a 3'-position phosphate for the functioning of mononucleotides as substrates for the enzyme. The enzyme had a molecular weight of 79 000, was stable at low temperatures and was thermally denatured at temperatures above 50 degrees C.     

Subcellular localizations of guanylate cyclase and 3',5'-cyclic nucleotide phosphodiesterase in sea urchin sperm.

The subcellular localizations of guanylate cyclase and 3',5'-cyclic nucleotide phosphodiesterase in sea urchin sperm were examined. Both the specific and total activities of these two enzymes were much higher in sperm flagella (tails) than in the heads. In addition to the observation that guanylate cyclase in the flagella was particulate-bound and solubilized by Triton X-100, more than 80% of the cyclase activity in the flagella was found in the plasma membrane fraction, whereas the activity of cyclic nucleotide phosphodiesterase was observed in both the axonemal and plasma membrane fractions. The observations indicated that the cyclase in the flagella appeared to be associated with the plasma membrane. Cyclic nucleotide phosphodiesterase in the plasma membrane fraction as well as the axonemal fraction hydrolyzed both cyclic GMP and cyclic AMP; however, the rates of hydrolysis for cyclic GMP were obviously higher than those for cyclic AMP. The enzymic properties of guanylate cyclase and cyclic nucleotide phosphodiesterase in sperm flagella were also briefly described.     

Calcium-dependent 3':5'-cyclic nucleotide phosphodiesterase. Inhibition of basal activity at physiological levels of potassium ions.

A calcium-dependent cyclic nucleotide phosphodiesterase from rat cerebrum was, in the absence of activator protein, inhibited by various monovalent cations. The inhibition was rapid, readily reversible, and concentration-dependent, with 100 mM cesium, rubidium, or potassium ion inhibiting essentially all basal enzyme activity, while 100 mM sodium or lithium ions produced only moderate inhibition. The potency of the cations in inhibiting the enzyme was Cs greater than or equal to Rb greater than K greater than Na greater than or equal to Li. Potassium ions increased the apparent Km for cyclic GMP and cyclic AMP by 3- and 5-fold, respectively. At 100 mM, the monovalent cations inhibited enzyme activated by the calcium-dependent activator by only 15 to 30%, while at 55 mM no inhibition pertained. Potassium and sodium ions at 55 mM had no effect on the calcium-independent phosphodiesterase from rat cerebrum. The results indicate that at normal intracellular concentrations of potassium ions the activity of the calcium-dependent phosphodiesterase is virtually completely dependent on the presence of calcium plus activator protein.     

Differences and similarities between guanosine 3',5'-cyclic monophosphate phosphodiesterase and adenosine 3',5'-cyclic monophosphate phosphodiesterase activities in neuroblastoma cells in culture.

There are phosphodiesterase activities in both particulate and supernatant fractions which hydrolyze guanosine 3',5'-cyclic monophosphate (cGMP) and adenosine 3',5'-cyclic monophosphate (cAMP) with an apparent Km of 2-8 muM and with an apparent Km of 44-222 muM. 4-(3-Butoxy-4-methoxybenzyl-2-imidazolidinone (RO20-1724) did not inhibit cGMP phosphodiesterase activity in homogenates of mouse neuroblastoma cells, but markedly inhibited cAMP phosphodiesterase activity. Papaverine and theophylline inhibited both cGMP and cAMP phosphodiesterase activities to about the same extent. The former was more potent than the latter. The specific activity of cGMP phosphodiesterase as a function of protein concentrations first increased and then decreased. The specific activity of cAMP phosphodiesterase decreased under a similar experimental condition.     

Demonstration, in leukemia L-1210 cells, of a phosphodiesterase acting on 3':5'-cyclic CMP but not on 3':5'-cyclic AMP or 3':5'-cyclic GMP.

cCMP-specific phosphodiesterase activity was demonstrated in the 80 to 100% ammonium sulfate fraction obtained from disrupted leukemia L-1210 cells. The activity was linear with time (up to 60 min), was a function of protein concentration, and was markedly stimulated by Mg2+ and by ammonium sulfate. Under identical assay conditions, no significant hydrolysis of cAMP or cGMP was observed, although these cyclic nucleotides served as substrates for phosphodiesterase(s) present in all the fractions obtained by less than 80% ammonium sulfate saturation. This is the first demonstration of a cCMP-specific phosphodiesterase.     

Structural similarities between the Ca2+-dependent regulatory proteins of 3':5'-cyclic nucleotide phosphodiesterase and actomyosin ATPase.

Results of studies of the Ca2+-dependent protein modulator of 3':5'-cyclic nucleotide phosphodiesterase isolated from bovine brain are presented which show its structural similarity to the Ca2+-binding subunit of muscle troponin. Both proteins have blocked NH2 termini, similar and characteristic ultraviolet absorption spectra, similar Ca2+-binding properties, very similar amino acid compositions, and co-migrate on sodium dodecyl sulfate-polyacrylamide gels. The primary structures of selected tryptic peptides isolated from bovine brain modulator protein are similar or identical with regions of the primary sequences of rabbit skeletal muscle and bovine cardiac muscle troponin C. Bovine brain modulator protein contains and unidentified ninhydrin-positive basic compound not found in muscle troponin C. An improved procedure is presented which yields 40 to 70 mg of modulator protein per kg of bovine brain.     

Insulin-sensitive adenosine 3',5'-cyclic monophosphate phosphodiesterase of hepatocyte plasma membrane.

Adenosine 3',5'-cyclic monophosphate phosphodiesterase (EC 3.1.4.17) has been investigated in rat liver as to its insulin sensitivity. Hormone action has been assayed in vitro on a liver homogenate purified by DEAE-cellulose column chromatography, on isolated hepatocytes, on isolated plasma membranes. The DEAE-cellulose chromatography purified homogenate showed no sensitivity to insulin, whereas isolated hepatocytes incubated in presence of insulin showed increased phosphodiesterase activity in a plasma membrane-containing fraction. The plasma membrane-bound enzyme, which shows both high and low affinity components, was significantly stimulated after hormonal treatment; this effect being dependent on a V increase of the low Km form.     

The Rv0805 gene from Mycobacterium tuberculosis encodes a 3',5'-cyclic nucleotide phosphodiesterase: biochemical and mutational analysis

Mycobacterium tuberculosis is an important human pathogen and has developed sophisticated mechanisms to evade the host immune system. These could involve the use of cyclic nucleotide-dependent signaling systems, since the M. tuberculosis genome encodes a large number of functional adenylyl cyclases. Using bioinformatic approaches, we identify, clone, and biochemically characterize the Rv0805 gene product, the first cyclic nucleotide phosphodiesterase identified in M. tuberculosis and a homologue of the cAMP phosphodiesterase present in Escherichia coli (cpdA). The Rv0805 gene product, a class III phosphodiesterase, is a member of the metallophosphoesterase family, and computational modeling and mutational analyses indicate that the protein possesses interesting properties not reported earlier in this class of enzymes. Mutational analysis of critical histidine and aspartate residues predicted to be essential for metal coordination reduced catalytic activity by 90-50%, and several mutant proteins showed sigmoidal kinetics with respect to Mn in contrast to the wild-type enzyme. Mutation of an asparagine residue in the GNHD motif that is conserved throughout the metallophosphoesterase enzymes almost completely abolished catalytic activity, and these studies therefore represent the first mutational analysis of this class of phosphodiesterases. The Rv0805 protein hydrolyzes cAMP and cGMP in vitro, and overexpression in Mycobacterium smegmatis and E. coli reduces intracellular cAMP levels. The presence of an orthologue of Rv0805 in Mycobacterium leprae suggests that the Rv0805 protein could have an important role to play in regulating cAMP levels in these bacteria and adds an additional level of complexity to cyclic nucleotide signaling in this organism.