Cyclic GMP (cGMP) is the primary intracellular messenger for the visual signaling pathway in rod and cone photoreceptor cells of the retina. Light stimulation causes the activation of the cGMP phosphodiesterase (PDE6), the central effector of this biochemical pathway, and a transient lowering of cGMP concentration that generates the electrical response. Precise regulation of the lifetime of PDE6 activation is required to control the sensitivity, amplitude and kinetics of the light response. While the basic pathway of phototransduction is well established, important aspects of the activation and regulation of PDE6 remain unknown, including a detailed understanding of how PDE6 is inhibited by its gamma subunit and how activation of PDE6 by transducin occurs. Other proteins are known to interact with PDE6 in photoreceptor cells, but their purpose is unclear. Visual impairment and retinal degenerative disease (e.g., retinitis pigmentosa) are known to result from mutations in the genes coding for PDE6 subunits, and it is also known that genetic defects in PDE6 interacting proteins also can cause retinal degeneration and/or visual dysfunction. Furthermore, the increasing therapeutic reliance on PDE5 inhibitors (e.g., Viagra) raises concerns about adverse effects on the closely related photoreceptor PDE6 enzyme and its ability to control cGMP levels during visual signaling. Advancing our understanding at the molecular level of the structure, function, regulation, and pharmacology of PDE6 will permit effective treatments to be devised to slow, halt, and (ultimately) reverse the deterioration of vision in patients afflicted with visual disorders and progressive retinal degenerative diseases resulting from genetic defects in PDE6 and its network of interacting proteins. The three specific aims of the project are to understand: (a) the sequence by which inhibition by the gamma-subunit of PDE6 is relieved when transducin activates the PDE6 holoenzyme during visual excitation;(b) how the structural differences between PDE5 and PDE6 can reveal functional differences in drug binding, allosteric regulation and functional protein expression;and (c) the network of PDE6-interacting proteins and the function they play in modulating PDE6 and the photoresponse.

Public Health Relevance

The visual signaling pathway in rod and cone photoreceptors depends on the proper functioning and regulation of the cGMP phosphodiesterase enzyme (PDE6) during the transformation of a light stimulus into an electrical response. Genetic defects in PDE6 or therapeutic agents (e.g., erectile dysfunction drugs) that adversely affect PDE6 activity can lead to vision impairment, retinal degenerative diseases (e.g., retinitis pigmentosa, congenital stationary night-blindness), or total blindness. The proposed research will advance our understanding of the function, regulation, and pharmacology of PDE6 that will be important for developing new therapies to treat retinal diseases.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
Project #
Application #
Study Section
Biology and Diseases of the Posterior Eye Study Section (BDPE)
Program Officer
Mariani, Andrew P
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of New Hampshire
Schools of Earth Sciences/Natur
United States
Zip Code
Zeng-Elmore, Xiaohui; Gao, Xiong-Zhuo; Pellarin, Riccardo et al. (2014) Molecular architecture of photoreceptor phosphodiesterase elucidated by chemical cross-linking and integrative modeling. J Mol Biol 426:3713-3728
Zhang, Xiu-Jun; Gao, Xiong-Zhuo; Yao, Wei et al. (2012) Functional mapping of interacting regions of the photoreceptor phosphodiesterase (PDE6) ýý-subunit with PDE6 catalytic dimer, transducin, and regulator of G-protein signaling9-1 (RGS9-1). J Biol Chem 287:26312-20
Cahill, Karyn B; Quade, Jonathan H; Carleton, Karen L et al. (2012) Identification of amino acid residues responsible for the selectivity of tadalafil binding to two closely related phosphodiesterases, PDE5 and PDE6. J Biol Chem 287:41406-16
Matte, Suzanne L; Laue, Thomas M; Cote, Rick H (2012) Characterization of conformational changes and protein-protein interactions of rod photoreceptor phosphodiesterase (PDE6). J Biol Chem 287:20111-21
Cahill, Karyn B; Cote, Rick H (2011) Phosphodiesterase 6C, cGMP-specific cone alpha'. AFCS Nat Mol Pages 2011:
Gitschier, Hannah J; Cote, Rick H (2011) Phosphodiesterase 6D, cGMP-specific rod delta. AFCS Nat Mol Pages 2011:
Zhang, Xiu-Jun; Skiba, Nikolai P; Cote, Rick H (2010) Structural requirements of the photoreceptor phosphodiesterase gamma-subunit for inhibition of rod PDE6 holoenzyme and for its activation by transducin. J Biol Chem 285:4455-63
Liu, Yu-Ting; Matte, Suzanne L; Corbin, Jackie D et al. (2009) Probing the catalytic sites and activation mechanism of photoreceptor phosphodiesterase using radiolabeled phosphodiesterase inhibitors. J Biol Chem 284:31541-7
Zhang, Xiu-Jun; Cahill, Karyn B; Elfenbein, Arye et al. (2008) Direct allosteric regulation between the GAF domain and catalytic domain of photoreceptor phosphodiesterase PDE6. J Biol Chem 283:29699-705
Pentia, Dana C; Hosier, Suzanne; Cote, Rick H (2006) The glutamic acid-rich protein-2 (GARP2) is a high affinity rod photoreceptor phosphodiesterase (PDE6)-binding protein that modulates its catalytic properties. J Biol Chem 281:5500-5

Showing the most recent 10 out of 19 publications