Project description:Rod cGMP phosphodiesterase 6 (PDE6) is a key enzyme of the phototransduction cascade, consisting of PDE6alpha, PDE6beta, and two regulatory PDE6gamma subunits. PDE6 is membrane associated through isoprenyl membrane anchors attached to the C-termini of PDE6alpha and PDE6beta and can form a complex with prenyl-binding protein delta (PrBP/delta), an isoprenyl-binding protein that is highly expressed in photoreceptors. The stoichiometry of PDE6-PrBP/delta binding and the mechanism by which the PDE6-PrBP/delta complex assembles have not been fully characterized, and the location of regulatory PDE6gamma subunits within the protein assembly has not been elucidated. To clarify these questions, we have developed a rapid purification method for PDE6-PrBP/delta from bovine rod outer segments utilizing recombinant PrBP/delta. Transmission electron microscopy of negatively stained samples revealed the location of PrBP/delta and, thus, where the carboxyl-termini of PDE6alpha and PDE6beta must be located. The three-dimensional structure of the PDE6alphabetagamma complex was determined up to 18 A resolution from single-particle projections and was interpreted by model building to identify the probable location of isoprenylation, PDE6gamma subunits, and catalytic sites.
Project description:cGMP was first discovered in urine, demonstrating that kidney cells extrude this cyclic nucleotide. Drosophila Malpighian tubules provide a model renal system in which a homologue of mammalian PDE (phosphodiesterase) 6 is expressed. In humans, this cG-PDE (cGMP-specific PDE) is specifically expressed in the retinal system, where it controls visual signal transduction. In order to gain insight into the functional role of DmPDE6 (Drosophila PDE6-like enzyme) in epithelial function, we generated transgenic animals with targeted expression of DmPDE6 to tubule Type I (principal) cells. This revealed localization of DmPDE6 primarily at the apical membranes. As expected, overexpression of DmPDE6 resulted in elevated cG-PDE activity and decreased tubule cGMP content. However, such targeted overexpression of DmPDE6 creates a novel phenotype that manifests itself in inhibition of the active transport and efflux of cGMP by tubules. This effect is specific to DmPDE6 action, as no effect on cGMP transport is observed in tubules from a bovine PDE5 transgenic line which display reduced rates of fluid secretion, an effect not seen in DmPDE6 transgenic animals. Specific ablation of DmPDE6 in tubule principal cells, via expression of a targeted DmPDE6 RNAi (RNA interference) transgene, conferred increased active transport of cGMP, confirming a direct role for DmPDE6 in regulating cGMP transport in tubule principal cells. Pharmacological inhibition of DmPDE6 in wild-type tubules using the cG-PDE inhibitor, zaprinast, similarly results in stimulated cGMP transport. We provide the first demonstration of a novel role for a cG-PDE in modulating cGMP transport and efflux.
Project description:cGMP has been implicated in the regulation of many essential functions in the brain, such as synaptic plasticity, phototransduction, olfaction, and behavioral state. Cyclic nucleotide phosphodiesterase (PDE) hydrolysis of cGMP is the major mechanism underlying the clearance of cGMP and is likely to be important in any process that depends on intracellular cGMP. PDE9A has the highest affinity for cGMP of any PDE, and here we studied the localization of this enzyme in the rat brain using in situ hybridization. PDE9A mRNA is widely distributed throughout the brain with varying regional expression. The pattern of PDE9A mRNA expression closely resembles that of soluble guanylyl cyclase (sGC) in the rat brain, suggesting a possible functional association or coupling of these two enzymes in the regulation of cGMP levels. Most of the brain areas expressing PDE9A mRNA also contain neuronal nitric oxide synthase (NOS), the enzymatic source of NO and the principal activator of sGC. PDE9A is the only cGMP-specific PDE with significant expression in the forebrain, and as such is likely to play an important role in NO-cGMP signaling.
Project description:Sensory photoreceptors elicit vital physiological adaptations in response to incident light. As light-regulated actuators, photoreceptors underpin optogenetics, which denotes the noninvasive, reversible, and spatiotemporally precise perturbation by light of living cells and organisms. Of particular versatility, naturally occurring photoactivated adenylate cyclases promote the synthesis of the second messenger cAMP under blue light. Here, we have engineered a light-activated phosphodiesterase (LAPD) with complementary light sensitivity and catalytic activity by recombining the photosensor module of Deinococcus radiodurans bacterial phytochrome with the effector module of Homo sapiens phosphodiesterase 2A. Upon red-light absorption, LAPD up-regulates hydrolysis of cAMP and cGMP by up to sixfold, whereas far-red light can be used to down-regulate activity. LAPD also mediates light-activated cAMP and cGMP hydrolysis in eukaryotic cell cultures and in zebrafish embryos; crucially, the biliverdin chromophore of LAPD is available endogenously and does not need to be provided exogenously. LAPD thus establishes a new optogenetic modality that permits light control over diverse cAMP/cGMP-mediated physiological processes. Because red light penetrates tissue more deeply than light of shorter wavelengths, LAPD appears particularly attractive for studies in living organisms.
Project description:Cyclic guanosine monophosphate (cGMP) is a second messenger molecule that transduces nitric-oxide- and natriuretic-peptide-coupled signalling, stimulating phosphorylation changes by protein kinase G. Enhancing cGMP synthesis or blocking its degradation by phosphodiesterase type 5A (PDE5A) protects against cardiovascular disease. However, cGMP stimulation alone is limited by counter-adaptions including PDE upregulation. Furthermore, although PDE5A regulates nitric-oxide-generated cGMP, nitric oxide signalling is often depressed by heart disease. PDEs controlling natriuretic-peptide-coupled cGMP remain uncertain. Here we show that cGMP-selective PDE9A (refs 7, 8) is expressed in the mammalian heart, including humans, and is upregulated by hypertrophy and cardiac failure. PDE9A regulates natriuretic-peptide- rather than nitric-oxide-stimulated cGMP in heart myocytes and muscle, and its genetic or selective pharmacological inhibition protects against pathological responses to neurohormones, and sustained pressure-overload stress. PDE9A inhibition reverses pre-established heart disease independent of nitric oxide synthase (NOS) activity, whereas PDE5A inhibition requires active NOS. Transcription factor activation and phosphoproteome analyses of myocytes with each PDE selectively inhibited reveals substantial differential targeting, with phosphorylation changes from PDE5A inhibition being more sensitive to NOS activation. Thus, unlike PDE5A, PDE9A can regulate cGMP signalling independent of the nitric oxide pathway, and its role in stress-induced heart disease suggests potential as a therapeutic target.
Project description:The physiological effects of cGMP are largely determined by the activities of intracellular receptors, including cGMP-dependent protein kinase (PKG) and cGMP-binding cyclic nucleotide phosphodiesterases (PDEs), and the distribution of cGMP among these receptors dictates activity of the signalling pathway. In the present study, the effects of PKG-Ialpha or PKG-Ibeta on the rate of cGMP hydrolysis by the isolated PDE5 catalytic domain were examined. PKG-Ialpha strongly inhibited cGMP hydrolysis with an IC(50) value of 217 nM, which is similar to the physiological concentration of PKG in pig coronary artery reported previously. By contrast, PKG-Ibeta, which has lower affinity for cGMP than does PKG-Ialpha, inhibited cGMP hydrolysis with an IC(50) of approx. 1 microM. Inhibition by PKG-Ialpha was more effective than that by PKG-Ibeta, consistent with their relative affinities for cGMP. Autophosphorylation of PKGs increased their cGMP-binding affinities and their inhibitory effects on PDE5 hydrolysis of cGMP. Autophosphorylation of PKG-Ibeta increased its inhibitory potency on PDE5 hydrolysis of cGMP by 10-fold compared with a 2-fold increase upon autophosphorylation of PKG-Ialpha. The results indicate that cGMP bound to allosteric cGMP-binding sites of PKG is protected from hydrolysis by PDE5 and that persistent protection of cGMP by either non-phosphorylated or autophosphorylated PKGs may be a positive-feedback control to sustain cGMP signalling.
Project description:The alpha and beta tubulins compose the microtubule cytoskeleton which is involved in many cellular processes such as vesicular transport. The photoreceptor cells in the retina are neurons specialized for phototransduction. Here we report a novel interaction between tubulin and the photoreceptor cGMP phosphodiesterase (PDE6) gamma subunit (PDE gamma). The specificity and molecular details of the PDE gamma:tubulin interaction were analyzed through the experiments of pull down, microtubule co-sedimentation, and NMR spectroscopy. The tubulin-interacting site was identified to be in the PDE gamma C-terminal I67-G85 region, and the interaction interface appeared to be distinct from those with the other PDE gamma targets in phototransduction. We also observed that PDE gamma interacted with tubulin in a GTP-dependent manner. Our findings offer implications for non-phototransduction role(s) of PDE gamma in the photoreceptor neurons.
Project description:3',5'-cyclic guanosine monophosphate (cGMP) is a druggable second messenger regulating cell growth and survival in a plethora of cells and disease states, many of which are associated with hypoxia. For example, in myocardial infarction and heart failure (HF), clinical use of cGMP-elevating drugs improves disease outcomes. Although they protect mice from ischemia/reperfusion (I/R) injury, the exact mechanism how cardiac cGMP signaling is regulated in response to hypoxia is still largely unknown. By monitoring real-time cGMP dynamics in murine and human cardiomyocytes using in vitro and in vivo models of hypoxia/reoxygenation (H/R) and I/R injury combined with biochemical methods, we show that hypoxia causes rapid but partial degradation of cGMP-hydrolyzing phosphodiesterase-3A (PDE3A) protein via the autophagosomal-lysosomal pathway. While increasing cGMP in hypoxia prevents cell death, partially reduced PDE3A does not change the pro-apoptotic second messenger 3',5'-cyclic adenosine monophosphate (cAMP). However, it leads to significantly enhanced protective effects of clinically relevant activators of nitric oxide-sensitive guanylyl cyclase (NO-GC). Collectively, our mouse and human data unravel a new mechanism by which cardiac cGMP improves hypoxia-associated disease conditions.