An oxygen-sensing diguanylate cyclase and phosphodiesterase couple for c-di-GMP control

A commonly observed coupling of sensory domains to GGDEF-class diguanylate cyclases and EAL-class phosphodiesterases has long suggested that c-di-GMP synthesizing and degrading enzymes sense environmental signals. Nevertheless, relatively few signal ligands have been identified for these sensors, and even fewer instances of in vitro switching by ligand have been demonstrated. Here we describe an Escherichia coli two-gene operon, dosCP, for control of c-di-GMP by oxygen. In this operon, the gene encoding the oxygen-sensing c-di-GMP phosphodiesterase Ec Dos (here renamed Ec DosP) follows and is translationally coupled to a gene encoding a diguanylate cyclase, here designated DosC. We present the first characterizations of DosC and a detailed study of the ligand-dose response of DosP. Our results show that DosC is a globin-coupled sensor with an apolar but accessible heme pocket that binds oxygen with a K(d) of 20 microM. The response of DosP activation to increasing oxygen concentration is a complex function of its ligand saturation such that over 80% of the activation occurs in solutions that exceed 30% of air saturation (oxygen >75 microM). Finally, we find that DosP and DosC associate into a functional complex. We conclude that the dosCP operon encodes two oxygen sensors that cooperate in the controlled production and removal of c-di-GMP.

Nitric oxide-sensitive guanylate cyclase activity is associated with the maturational phase of neuronal development in insects

Many developing insect neurones pass through a phase when they respond to nitric oxide (NO) by producing cyclic GMP. Studies on identified grasshopper motoneurones show that this NO sensitivity appears after the growth cone has arrived at its target but before it has started to send out branches. NO sensitivity typically ends as synaptogenesis is nearing completion. Data from interneurones and sensory neurones are also consistent with the hypothesis that NO sensitivity appears as a developing neurone changes from axonal outgrowth to maturation and synaptogenesis. Cyclic GMP likely constitutes part of a retrograde signalling pathway between a neurone and its synaptic partner. NO sensitivity also appears in some mature neurones at times when they may be undergoing synaptic rearrangement. Comparative studies on other insects indicate that the association between an NO-sensitive guanylate cyclase and synaptogenesis is an ancient one, as evidenced by its presence in both ancient and more recently evolved insect groups.

Single-step affinity purification, partial structure and properties of human platelet cGMP inhibited cAMP phosphodiesterase

The human platelet cilostamide- and cGMP-inhibited cAMP phosphodiesterase (cGI-PDE) was rapidly purified approximately 19,000-fold to apparent homogeneity using single step affinity chromatography on the isothiocyanate derivative of cilostamide coupled to aminoethyl agarose. Within 24 h, 30 micrograms of enzyme protein was obtained from 20 ml of packed platelets. Vmax for cAMP and cGMP was 6.1 and 0.9 mumol/min per mg protein, respectively. Several polypeptides (110/105, 79, 62, 55/53 kDa) were identified after SDS-PAGE, all of which were immunologically related to cGI-PDE and represented approx. 5, 20, 50 and 20% of the total protein, respectively. Limited proteolysis of the cGI-PDE with chymotrypsin produced a major fragment of approximately 47 kDa (and at least two smaller peptides) with catalytic activity and sensitivity to cGMP and OPC 3911 similar to controls. Phosphorylation of the cGI-PDE by cAMP-dependent protein kinase (A-kinase) resulted in maximal incorporation of 0.6-1.8 mol of 32P/mol 110/105 and 79 kDa polypeptides; much lower and variable amounts of phosphate were incorporated into the 62 and 55/53 kDa polypeptides. After digestion of cGI-PDE with several proteinases a number of peptides were isolated and sequenced. Most of the peptide sequences obtained could be aligned within the carboxy terminal domain of the deduced sequence of the human cardiac cGI-PDE. These and other results suggest that the subunit size of the intact platelet cGI-PDE is 110 kDa and that proteolytic fragments of 79, 62 and 55/53 kDa are produced during purification. The smaller fragments (62 and 55/53 kDa) contain the catalytic domain; the larger fragments (110 and 79 kDa) also contain the regulatory domain with phosphorylation sites for A-kinase.

Purification of 125I-labeled succinyl cyclic nucleotide tyrosine methyl esters by high-performance liquid chromatography

Carrier free 125I-labeled succinyl cyclic adenosine monophosphate (ScAMP) and succinyl cyclic guanosine monophosphate (ScGMP) tyrosine methyl esters (TME) were purified by reversed phase high-performance liquid chromatography (HPLC) or descending paper chromatography. Using an isocratic buffer for HPLC, mono-ScAMP-125I-TME and mono-ScGMP-125I-TME were eluted from a C18 column at 8.9 and 6.9 min, respectively. Both of the mono-iodinated radioligands were completely separated from their noniodinated precursors and other iodinated products. The radioligands purified by HPLC or paper chromatography were used for the radioimmunoassay (RIA) of cAMP and cGMP. Cyclic AMP or cGMP inhibited binding of the HPLC purified radioligands at three- to fivefold lower concentrations than the paper chromatography purified radioligands. The sensitivity of the RIA decreased with time if paper chromatography purified radioligands were used, but remained stable for 4 months if the HPLC purified compounds were used, even with storage at 4 degrees C. We attribute these results to better purification of radioligands by the HPLC than by the paper chromatography. Using optimal conditions the HPLC method takes only 10 min and results in a high yield (greater than 95%) of added 125I into the monoiodinated products.

Cyclic nucleotide content of tobacco BY-2 cells

The cyclic nucleotide content of cultured tobacco bright yellow-2 (BY-2) cells was determined, after freeze-killing, perchlorate extraction and sequential chromatography, by radioimmunoassay. The identities of the putative cyclic nucleotides, adenosine 3',5'-cyclic monophosphate (cyclic AMP), guanosine 3',5'-cyclic monophosphate (cyclic GMP) and cytidine 3',5'-cyclic monophosphate (cyclic CMP) were unambiguously confirmed by tandem mass spectrometry. The potential of BY-2 cell cultures as a model system for future investigations of cyclic nucleotide function in higher plants is discussed.

Measurement of adenosine 3',5'-cyclic monophosphate and guanosine 3', 5'-cyclic monophosphate in mussel (Mytilus galloprovincialis lmk.) by high-performance liquid chromatography with diode array detection

Two fast and sensitive methods for the determination of cAMP and cGMP levels in mantle tissue of the sea mussel Mytilus galloprovincialis Lmk. are described. Both methods use ion-pair high-performance liquid chromatography with diode array detection. The use of the diode array detector permitted the simultaneous detection of the absorbance at two different wavelengths and the obtaining of the UV absorption spectrum for each detected peak, confirming peak purity and identity. Method precision was good. The detection limit for both nucleotides was 2.5 pmol (signal-to-noise ratio = 4 at 254 nm). Previous to the injection onto the chromatograph, both nucleotides were purified by precipitation of the adenine and guanine 5'-ribonucleotides with ZnSO(4)-Na(2)CO(3). The supernatant obtained was subsequently passed over an anion-exchange column (AG l-X8 formate form resin). Early results seem to indicate that there is a seasonal variation in the contents of both cyclic nucleotides in mantle tissue. Such variation is probably related to the annual gametogenic cycle.

Effect of acetylcholine on the norepinephrine-induced positive chronotropy and increase in cyclic nucleotides of isolated rabbit sinoatrial node

Transmural stimulation of, or application of nicotine to, the isolated rabbit sinoatrial (SA) node resulted in initial negative and late positive chronotropy. Simultaneous application of acetylcholine and norepinephrine produced a similar biphasic chronotropic effect. These procedures produced an initial increase in cyclic guanosine 3':5'-monophosphate (cyclic GMP) and a delayed elevation in cyclic adenosine 3':5'-monophosphate (cyclic AMP). The initial and late effects on rate and nucleotide levels were inhibited by pretreatment with atropine and propranolol, respectively. Pretreatment with atropine shortened the time of maximum increase in cyclic AMP level and heart rate from 3 to 1 minute after the simultaneous application of acetylcholine and norepinephrine and enhanced the positive chronotropic effect. Physostigmine prolonged the duration of the increase in cyclic GMP and negative chronotropic effect after the simultaneous application. These results suggest that when acetylocholine and norepinephrine are present simultaneously in the SA node region, the former interacts predominantly with muscarinic receptors and stimulates the cyclic GMP system, which in effect delays the cyclic AMP elevation and reduces the positive chronotropic effect of norepinephrine. However, these effects of acetylcholine cannot be explained solely on the basis of changes in the cyclic GMP level, because sodium nitroprusside produced a marked elevation of the cyclic GMP levels without decreasing the heart rate and did not affect the norepinephrine-induced increase in pacemaker rate and cyclic AMP. Sodium nitroprusside may affect cyclic GMP pools other than those susceptible to acetylcholine. These cyclic GMP pools may not exert chronotropic effects.

Cyclic GMP recognition using ratiometric QD-fluorophore conjugate nanosensors

Novel luminescent ratiometric nanosensors (QD-NAPTHs) were prepared based on cadmium telluride (CdTe655) quantum dots as luminescent nanoscaffolds with naphthyridine dyes as fluorescent receptors. This biosensing bifluorophoric nanosystem has been designed to achieve detection of guanosine 3',5'-cyclic monophosphate (cyclic GMP) in buffered media. Cyclic GMP is a secondary messenger that is an important factor for detecting cancer, diabetes and, cardiovascular diseases. Due to low concentration levels, even in pathological conditions, sensitive cGMP detection remains a challenge for modern biomedical diagnostics. Here, QD-NAPTH nanosensors were tested in the presence of a target nucleotide and with various structural cGMP analogues. Steady-state fluorescence spectroscopy was used to monitor a change in the nucleotide concentration. A 5-fold increase in naphthyridine fluorescence with a simultaneous decrease in QD luminescence was observed after adding 50 μM of cGMP. Using this novel nanosystem with ratiometric detection, it was possible to recognize cGMP with limit of detection (3σ) equal to 70 ng/ml. Moreover, the enhancement in fluorescence upon interaction with the target nucleotide constitutes a favourable approach towards the detection of cGMP in buffered media. These bifluorophoric nanosensors have a potential for application in fluorescence microscopy imaging and in-vitro assays.

Epinephrine-induced elevation of guanosine 3':5'-cyclic monophosphate in isolated fat cells of rat

The effects of epinephrine (as low as 0.1 muM) on guanosine 3':5'-cyclic monophosphate (cGMP) and adenosine 3':5'-cyclic monophosphate (cAMP) in isolated fat cells were examined. Epinephrine increased both cGMP and cAMP levels, with the elevation of cAMP preceding the rise of cGMP. Maximal elevation was obtained with 1 muM epinephrine for each nucleotide. The increase in content of cGMP and cAMP due to epinephrine was completely blocked by a beta-adrenergic antagonist (5 muM propranolol). Phentolamine (10-100 muM), an alpha-adrenergic antagonist, enhanced the response to epinephrine resulting in elevation of cAMP levels, whereas a high concentration (100 muM) of phentolamine suppressed the elevation of cGMP. The ability of epinephrine to increase cGMP and cAMP levels was markedly diminished by "feedback regulator" partially purified from the incubation mixtures of isolated fat cells exposed to epinephrine [Ho, R.J. & Sutherland, E. W. (1971) J. Biol. Chem. 246, 6822-6827], whereas an increase in cGMP, but not cAMP, levels was observed in isolated fat cells incubated with "feedback regulator" alone (without epinephrine). These observations suggest the possibility that the epinephrine-induced elevation of cGMP levels in isolated fat cells might be mediated by an increase in formation of intracellular "feedback regulator" due to an elevation of cAMP by epinephrine.