title: Structural determinants of phosphodiesterase 6 response on binding catalytic site inhibitors.
abstract: To predict the response of retinal phosphodiesterase on binding catalytic site inhibitors, a homology model of the catalytic domain of subunit alpha of type 6 phosphodiesterase has been built by selecting an experimental structure of type 5 phosphodiesterase as template. Guanosine monophosphate and inhibitors (sildenafil, zaprinast) docked to the type 6 phosphodiesterase binding crevice similarly to the experimental conformations of guanosine monophosphate and sildenafil in the catalytic domain of type 5 phosphodiesterase. Inhibitors, but not guanosine monophosphate, interacted with Phe778 and Met759 (sildenafil) or Met759 (zaprinast), the key residues involved in the interaction between the catalytic binding domain and the inhibitory gamma subunit of type 6 phosphodiesterase. Agreeing with predictions obtained by modelling binding, both inhibitors (1 and 10muM) enhanced the amplitude of electric light responses of the isolated rat retina, however, the enhancement was smaller for the more efficacious inhibitor sildenafil. These paradoxical responses can be explained as a result of the enhancement of light activation of PDE6 through the competition between the catalytic site inhibitors and the gamma subunit residues for catalytic domain residues Phe778 and Met759.
authors.affiliation: Department of Neurochemistry, Chemical Research Center, Hungarian Academy of Sciences, Pusztaszeri út 59-67, H-1025 Budapest, Hungary. simonagi@chemres.hu
authors.forename: Agnes
authors.initials: A
authors.lastname: Simon
authors.forename: Péter
authors.initials: P
authors.lastname: Barabás
authors.forename: Julianna
authors.initials: J
authors.lastname: Kardos
mesh_terms: D000595:Amino Acid Sequence / Q000502:physiology; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D020134:Catalytic Domain / Q000187:drug effects / Q000502:physiology*; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D017386:Sequence Homology, Amino Acid
chemical_list: D010726:Phosphodiesterase Inhibitors; D010727:Phosphoric Diester Hydrolases; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; C517431:PDE6B protein, human