The long-term goal of this research program is to elucidate the molecular mechanisms of the function and regulation of rod and cone cGMP-phosphodiesterases (PDE6). PDE6s serve as key effector enzymes in the vertebrate visual transduction cascade. Transducin activates PDE6 by relieving the inhibition imposed on the PDE6 catalytic dimer by two ?-subunits (P3). Rod PDE6 is unique among cyclic nucleotide PDEs in that it is a catalytic heterodimer composed of the PDE6A and PDE6B catalytic subunitsWe hypothesize that the heterodimerization of rod PDE6 plays an important role in rod phototransduction. The individual properties of PDE6A and PDE6B and the functional significance of rod PDE6 heterodimerization will be examined in aim 1. The goal is to bring a new level of understanding to the mechanism of rod PDE6 activation by transducin and advance the current models of the rod phototransduction cascade. Based on the existing evidence and our preliminary studies, we hypothesize that the interaction of P? with the PDE6 catalytic subunits is critical to the proper transport of the holoenzyme in photoreceptor cells.
Aim 2 is to test this hypothesis and probe the mechanisms of P? in expression and transport of PDE6.
Aims 1 and 2 will be achieved through extensive use of transgenic Xenopus laevis as a novel approach for the expression of mutant PDE6. Mutations in the human PDE6A and PDE6B genes each are responsible for 3-4% of cases of recessive retinitis pigmentosa (RP).
As aim 3 we will investigate the mechanism of the recessive mutation N605S in the mouse PDE6B subunit causing atypical retinal degeneration (atrd3) in mice. Based on the initial evidence, we hypothesize that atrd3 is triggered by functional changes in PDE6 and may reflect certain forms and mechanisms of human RP. The atrd3 mechanism will be examined using the mutant mouse model in comparison to a transgenic Xenopus laevis model of the cone PDE6C mutant counterpart. The molecular details of PDE6 inhibition by its ?-subunit will be elucidated by means of protein crystallography in aim 4. The structure of the chimeric PDE5/6 catalytic domain complexed with P?-63-87 and sildenafil (Viagra) will provide the first structural insights into the critical interaction between PDE6 and P? and should reveal the structural basis for the side effects of Viagra on vision. The structure of the chimeric atrd3 mutant will be investigated to uncover the molecular mechanism for retinal disease associated with this PDE6 mutation. Overall, these studies will advance our understanding of the regulation of PDE6 and help to elucidate the mechanisms of RP caused by mutations of PDE6 genes.

Public Health Relevance

Rod and cone cGMP phosphodiesterases (PDE6 family) are the key effector enzymes in vision. Mutations in PDE6 lead to human retinal diseases such as retinitis pigmentosa, congenital stationary night blindness, and achromatopsia. This research would develop a new level of understanding of structure, function, and regulation of PDE6 necessary to uncover the mechanisms of PDE6 mutations in diseased retina.

National Institute of Health (NIH)
National Eye Institute (NEI)
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Biology and Diseases of the Posterior Eye Study Section (BDPE)
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Mariani, Andrew P
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University of Iowa
Schools of Medicine
Iowa City
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Yu, Liping; Yadav, Ravi P; Artemyev, Nikolai O (2018) NMR resonance assignments of the TPR domain of human aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1). Biomol NMR Assign :
Wang, Tian; Reingruber, J├╝rgen; Woodruff, Michael L et al. (2018) The PDE6 mutation in the rd10 retinal degeneration mouse model causes protein mislocalization and instability and promotes cell death through increased ion influx. J Biol Chem 293:15332-15346
Pahlberg, Johan; Majumder, Anurima; Artemyev, Nikolai O (2018) Ex Vivo Functional Evaluation of Synaptic Transmission from Rods to Rod Bipolar Cells in Mice. Methods Mol Biol 1753:203-216
Yadav, Ravi P; Gakhar, Lokesh; Yu, Liping et al. (2017) Unique structural features of the AIPL1-FKBP domain that support prenyl lipid binding and underlie protein malfunction in blindness. Proc Natl Acad Sci U S A 114:E6536-E6545
Gopalakrishna, Kota N; Boyd, Kimberly; Artemyev, Nikolai O (2017) Mechanisms of mutant PDE6 proteins underlying retinal diseases. Cell Signal 37:74-80
Yadav, Ravi P; Artemyev, Nikolai O (2017) AIPL1: A specialized chaperone for the phototransduction effector. Cell Signal 40:183-189
Yu, Liping; Yadav, Ravi P; Artemyev, Nikolai O (2017) NMR resonance assignments of the FKBP domain of human aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) in complex with a farnesyl ligand. Biomol NMR Assign 11:111-115
Gopalakrishna, Kota N; Boyd, Kimberly; Yadav, Ravi P et al. (2016) Aryl Hydrocarbon Receptor-interacting Protein-like 1 Is an Obligate Chaperone of Phosphodiesterase 6 and Is Assisted by the ?-Subunit of Its Client. J Biol Chem 291:16282-91
Yadav, Ravi P; Majumder, Anurima; Gakhar, Lokesh et al. (2015) Extended conformation of the proline-rich domain of human aryl hydrocarbon receptor-interacting protein-like 1: implications for retina disease. J Neurochem 135:165-75
Majumder, Anurima; Pahlberg, Johan; Muradov, Hakim et al. (2015) Exchange of Cone for Rod Phosphodiesterase 6 Catalytic Subunits in Rod Photoreceptors Mimics in Part Features of Light Adaptation. J Neurosci 35:9225-35

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