Regulation of photoreceptor phosphodiesterase catalysis by its non-catalytic cGMP-binding sites

D'Amours, Marc R.; Cote, Rick H.

doi:10.1042/bj3400863

Cited by 30 publications

(20 citation statements)

References 40 publications

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“…Both tPDE and P␣␤ are stoichiometrically inhibited by 2 mol of P␥ per mol of P␣␤. The steep linear dependence of tPDE and P␣␤ activity on the P␥ concentration reflects a titration phenomenon consistent with the sub-nanomolar binding affinity of P␥ for frog PDE reported previously (22). The similar behavior for tPDE and P␣␤ in Fig.…”

Section: Two Distinct Classes Of P␥-binding Sites On P␣␤ Restoresupporting

confidence: 66%

“…It has also been proposed that changes in cGMP binding affinity to the noncatalytic sites during visual transduction might permit the release of bound cGMP to accelerate the restoration of cGMP levels during the recovery phase of the photoresponse (37,38). Finally, the idea that the noncatalytic sites on photoreceptor PDE might directly regulate hydrolysis of cGMP at the active site (as is the case for PDE2) has not been supported by current evidence (22,39).…”

mentioning

confidence: 81%

“…Non-activated PDE (nPDE) was obtained directly from nucleotide-depleted ROS homogenates; in the absence of GTP, dark-adapted and light-exposed ROS homogenates show no difference in the rate of cGMP hydrolysis or in the extent of cGMP binding. The catalytic activity of nPDE was typically 1-3% of the activated rate at the concentrations used in this paper (22). Transducinactivated PDE (taPDE) was prepared by incubating nucleotide-depleted ROS homogenates ([PDE] Ն12 nM; see Ref.…”

Section: Pde Preparations Used In Thismentioning

confidence: 99%

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Mechanism of Transducin Activation of Frog Rod Photoreceptor Phosphodiesterase

Norton

D'Amours

Grazio

et al. 2000

Journal of Biological Chemistry

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The rod photoreceptor phosphodiesterase (PDE) is unique among all known vertebrate PDE families for several reasons. It is a catalytic heterodimer (␣␤); it is directly activated by a G-protein, transducin; and its active sites are regulated by inhibitory ␥ subunits. Rod PDE binds cGMP at two noncatalytic sites on the ␣␤ dimer, but their function is unclear. We show that transducin activation of frog rod PDE introduces functional heterogeneity to both the noncatalytic and catalytic sites. Upon PDE activation, one noncatalytic site is converted from a high affinity to low affinity state, whereas the second binding site undergoes modest decreases in binding. Addition of ␥ to transducin-activated PDE can restore high affinity binding as well as reducing cGMP exchange kinetics at both sites. A strong correlation exists between cGMP binding and ␥ binding to activated PDE; dissociation of bound cGMP accompanies ␥ dissociation from PDE, whereas addition of either cGMP or ␥ to ␣␤ dimers can restore high affinity binding of the other molecule. At the active site, transducin can activate PDE to about one-half the turnover number for catalytic ␣␤ dimers completely lacking bound ␥ subunit. These results suggest a mechanism in which transducin interacts primarily with one PDE catalytic subunit, releasing its full catalytic activity as well as inducing rapid cGMP dissociation from one noncatalytic site. The state of occupancy of the noncatalytic sites on PDE determines whether ␥ remains bound to activated PDE or dissociates from the holoenzyme, and may be relevant to light adaptation in photoreceptor cells.Initiation of the phototransduction cascade in vertebrate rod photoreceptors by light results in the sequential activation of the visual pigment (rhodopsin), the photoreceptor G-protein (transducin), and the effector enzyme (cGMP phosphodiesterase (EC 3.1.4.35), PDE) 1 (for reviews see Refs. 1-4). The PDE present in rod and cone photoreceptors (classified as PDE6) differs in several ways from other classes of mammalian phosphodiesterases (5-7): rod photoreceptor PDE forms a catalytic dimer from two closely related ␣ and ␤ subunits (P␣␤); rod and cone PDE are directly regulated via heterotrimeric G-proteins. the catalytic constant (k cat ) for rod PDE is ϳ1000-fold greater than for any other class of PDE; the catalytic activity of photoreceptor PDE is potently inhibited by binding of an inhibitory ␥ subunit (P␥) (for reviews see Refs. 8 and 9). Transducin activation of PDE results from binding of the activated transducin ␣ t subunit (␣ t -GTP) to one or more sites on the PDE holoenzyme. One result of this interaction is the displacement of the inhibitory P␥ subunit from its binding site in the catalytic pocket of PDE. It is not clear, however, whether each PDE catalytic subunit binds P␥ with equal affinity, whether ␣ t -GTP can activate each catalytic site equally well, and under what conditions the ␣ t -GTP-P␥ complex dissociates from P␣␤. Conflicting results reported by different laboratories (10 -24) may reflect underlying...

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Section: Two Distinct Classes Of P␥-binding Sites On P␣␤ Restoresupporting

confidence: 66%

mentioning

confidence: 81%

Section: Pde Preparations Used In Thismentioning

confidence: 99%

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Mechanism of Transducin Activation of Frog Rod Photoreceptor Phosphodiesterase

Norton

D'Amours

Grazio

et al. 2000

Journal of Biological Chemistry

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“…P␥ proteins block catalytic activity by forming a tight complex (K D ϳ28 pM) with PDE6 catalytic subunits through contacts of a polycationic region with GAF-A and interaction with the catalytic site (10,136,264,267). cGMP binding to PDE6 GAF-A enhances P␥ binding (84). Light-activated transducin interacts with P␥ to relieve its effect.…”

Section: Gaf-containing Pdesmentioning

confidence: 99%

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

Francis

Blount

Corbin

2011

Physiological Reviews

560

546

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The superfamily of cyclic nucleotide (cN) phosphodiesterases (PDEs) is comprised of 11 families of enzymes. PDEs break down cAMP and/or cGMP and are major determinants of cellular cN levels and, consequently, the actions of cN-signaling pathways. PDEs exhibit a range of catalytic efficiencies for breakdown of cAMP and/or cGMP and are regulated by myriad processes including phosphorylation, cN binding to allosteric GAF domains, changes in expression levels, interaction with regulatory or anchoring proteins, and reversible translocation among subcellular compartments. Selective PDE inhibitors are currently in clinical use for treatment of erectile dysfunction, pulmonary hypertension, intermittent claudication, and chronic pulmonary obstructive disease; many new inhibitors are being developed for treatment of these and other maladies. Recently reported x-ray crystallographic structures have defined features that provide for specificity for cAMP or cGMP in PDE catalytic sites or their GAF domains, as well as mechanisms involved in catalysis, oligomerization, autoinhibition, and interactions with inhibitors. In addition, major advances have been made in understanding the physiological impact and the biochemical basis for selective localization and/or recruitment of specific PDE isoenzymes to particular subcellular compartments. The many recent advances in understanding PDE structures, functions, and physiological actions are discussed in this review.

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“…First, while the maximum rate of cGMP hydrolysis by PDE6 achieves catalytic perfection 17,18,7 (6000-8000 cGMP hydrolyzed per second) and operates at the diffusion-controlled limit, the catalytic constant for PDE5 is lower by almost three orders of magnitude. 19 This extraordinary catalytic power of PDE6 may have evolved from the need of photoreceptor cells to generate a receptor potential on the millisecond time scale.…”

Section: Similarities and Differences Between Pde5 And Pde6mentioning

confidence: 99%

Characteristics of Photoreceptor PDE (PDE6): similarities and differences to PDE5

2004

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Phosphodiesterase 6 (PDE6) is highly concentrated in the retina. It is most abundant in the internal membranes of retinal photoreceptors, where it reduces cytoplasmic levels of cyclic guanosine monophosphate (cGMP) in rod and cone outer segments in response to light. The rod PDE6 holoenzyme comprises a and b catalytic subunits and two identical inhibitory c subunits. Each catalytic subunit contains three distinct globular domains corresponding to the catalytic domain and two GAF domains (responsible for allosteric cGMP binding). The PDE6 catalytic subunits resemble PDE5 in amino-acid sequence as well as in three-dimensional structure of the catalytic dimer; preference for cGMP over cyclic adenosine monophosphate (cAMP) as a substrate; and the ability to bind cGMP at the regulatory GAF domains. Most PDE5 inhibitors inhibit PDE6 with similar potency, and electroretinogram studies show modest effects of PDE5 inhibitors on visual function-an observation potentially important in designing PDE5-specific therapeutic agents.

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Regulation of photoreceptor phosphodiesterase catalysis by its non-catalytic cGMP-binding sites

Cited by 30 publications

References 40 publications

Mechanism of Transducin Activation of Frog Rod Photoreceptor Phosphodiesterase

Mechanism of Transducin Activation of Frog Rod Photoreceptor Phosphodiesterase

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

Characteristics of Photoreceptor PDE (PDE6): similarities and differences to PDE5

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