title: Catalytic mechanism of a retinoid isomerase essential for vertebrate vision.
abstract: Visual function in vertebrates is dependent on the membrane-bound retinoid isomerase RPE65, an essential component of the retinoid cycle pathway that regenerates 11-cis-retinal for rod and cone opsins. The mechanism by which RPE65 catalyzes stereoselective retinoid isomerization has remained elusive because of uncertainty about how retinoids bind to its active site. Here we present crystal structures of RPE65 in complex with retinoid-mimetic compounds, one of which is in clinical trials for the treatment of age-related macular degeneration. The structures reveal the active site retinoid-binding cavity located near the membrane-interacting surface of the enzyme as well as an Fe-bound palmitate ligand positioned in an adjacent pocket. With the geometry of the RPE65-substrate complex clarified, we delineate a mechanism of catalysis that reconciles the extensive biochemical and structural research on this enzyme. These data provide molecular foundations for understanding a key process in vision and pharmacological inhibition of RPE65 with small molecules.
authors.affiliation: Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Kiser
authors.affiliation: Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Jianye
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Badiee
authors.affiliation: Department of Chemistry, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Qingjiang
authors.initials: Q
authors.lastname: Li
authors.affiliation: 1] National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, USA. [2] Case Center for Synchrotron Biosciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA..
authors.forename: Wuxian
authors.initials: W
authors.lastname: Shi
authors.affiliation: Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Xuewu
authors.initials: X
authors.lastname: Sui
authors.affiliation: Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Marcin
authors.initials: M
authors.lastname: Golczak
authors.affiliation: Department of Chemistry, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Tochtrop
authors.affiliation: Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Palczewski
mesh_terms: D000818:Animals; D001665:Binding Sites; D055162:Biocatalysis; D018360:Crystallography, X-Ray; D004224:Diterpenes / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D008024:Ligands; D008027:Light; D008810:Mice, Inbred C57BL; D062105:Molecular Docking Simulation; D015394:Molecular Structure; D010168:Palmitates; D010647:Phenyl Ethers / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D011412:Propanolamines / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000201:enzymology* / Q000528:radiation effects; D012176:Retinoids / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D013237:Stereoisomerism; D014785:Vision, Ocular / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D019745:cis-trans-Isomerases / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D000099178:Retinoid Isomerohydrolase
chemical_list: D004224:Diterpenes; D008024:Ligands; D010168:Palmitates; D010647:Phenyl Ethers; D011412:Propanolamines; D012176:Retinoids; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C000592692:emixustat; C009167:retinylamine