The molecular mechanism of dark noise in rod photoreceptors

Here we report a cryo-electron microscopy (cryoEM) structure of PDE6 complexed to GTP-bound GО±T. GTP) and the cyclic GMP (cGMP) phosphodiesterase 6 (PDE6), which stimulates cGMP hydrolysis, leading to hyperpolarization of the photoreceptor cell.In the phototransduction pathway responsible for vertebrate vision, the G protein-effector complex is composed of the GTP-bound transducin О± subunit (GО±T Heterotrimeric G proteins communicate signals from activated G protein-coupled receptors to downstream effector proteins. , CГ©lulas Fotorreceptoras Retinianas Bastonetes/quГmica , CГ©lulas Fotorreceptoras Retinianas Cones/quГmica , CГ©lulas Fotorreceptoras Retinianas Bastonetes/enzimologia , CГ©lulas Fotorreceptoras Retinianas Cones/enzimologia The therapeutic potential of pharmacological compounds acting as inhibitors or activators targeting PDE6 is discussed in the context of inherited retinal diseases resulting from mutations in rod and cone PDE6 genes as well as other inherited defects that arise from excessive cGMP accumulation in retinal photoreceptor cells.ДЄssuntos NucleotГdeo CГclico Fosfodiesterase do Tipo 6/metabolismo The role of the regulator of G-protein signaling 9-1 (RGS9-1) in regulating the lifetime of the transducin-PDE6 is also briefly covered. Emphasis is given to recent advances in understanding the structural and conformational changes underlying the mechanism by which the activated transducin О±-subunit binds to-and relieves inhibition of-PDE6 catalysis that is controlled by its intrinsically disordered, inhibitory ГЋВі-subunit. This review summarizes recent advances in the structural characterization of the rod and cone PDE6 catalytic and regulatory subunits in the context of previous biochemical studies of the enzymological properties and allosteric regulation of PDE6. Following cessation of the light stimulus, the lifetime of activated PDE6 is also precisely regulated by additional processes. Upon light stimulation, rapid activation of PDE6 by the heterotrimeric G-protein (transducin) triggers a dramatic drop in cGMP levels that lead to cell hyperpolarization. cGMP metabolism in the signal-transducing photoreceptor outer segment reflects the balance of cGMP synthesis (catalyzed by guanylyl cyclase) and degradation (catalyzed by the photoreceptor phosphodiesterase, PDE6). Rod and cone photoreceptors of the vertebrate retina utilize cGMP as the primary intracellular messenger for the visual signaling pathway that converts a light stimulus into an electrical response. , ProteГnas de LigaГ§ГЈo a Tacrolimo/metabolismo , Amaurose CongГЄnita de Leber/metabolismo , ProteГnas de Choque TГ©rmico HSP90/metabolismo , ProteГnas de Choque TГ©rmico HSP90/genГ©tica , NucleotГdeo CГclico Fosfodiesterase do Tipo 6/metabolismo , NucleotГdeo CГclico Fosfodiesterase do Tipo 6/quГmica , ProteГnas Adaptadoras de TransduГ§ГЈo de Sinal/metabolismo , ProteГnas Adaptadoras de TransduГ§ГЈo de Sinal/quГmica , NucleotГdeo CГclico Fosfodiesterase do Tipo 6 Thus, we conclude neither sequestration of the prenyl modifications is required for PDE6 maturation to proceed, nor is the FKBP-lipid interaction involved in the conformational switch of the enzyme into the functional state.ДЄssuntos ProteГnas Adaptadoras de TransduГ§ГЈo de Sinal Furthermore, AIPL1 was unexpectedly capable of inducing the maturation of unprenylated cone PDE6C, whereas mutant AIPL1 deficient in prenyl binding competently cochaperoned prenylated PDE6C. A mouse model with rod PDE6 lacking farnesylation of its PDE6A subunit revealed normal expression, trafficking, and signaling of the enzyme. In addition, the FK506-binding protein (FKBP) domain of AIPL1 encloses a unique prenyl-binding site that anchors AIPL1 to posttranslational lipid modifications of PDE6. We demonstrate that mutations of these determinants markedly diminished both the affinity of AIPL1 for HSP90 and the ability of AIPL1 to cochaperone the maturation of PDE6 in a heterologous expression system.

Our analysis suggests that AIPL1 preferentially binds to HSP90 in the closed state with a stoichiometry of 1:2, with the tetratricopeptide repeat domain and the tetratricopeptide repeat helix 7 extension of AIPL1 being the main contributors to the AIPL1/HSP90 interface. Here, we characterize the complex of AIPL1 with HSP90 and demonstrate its essential role in promoting the functional conformation of nascent PDE6. Defects in PDE6 and AIPL1 underlie several severe retinal diseases, including retinitis pigmentosa and Leber congenital amaurosis. Phosphodiesterase 6 (PDE6) is a key effector enzyme in vertebrate phototransduction, and its maturation and function are known to critically depend on a specialized chaperone, aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1).

The molecular mechanism of dark noise in rod photoreceptors