Kiser Philip D, Zhang Jianye, Badiee Mohsen, Li Qingjiang, Shi Wuxian, Sui Xuewu, Golczak Marcin, Tochtrop Gregory P, Palczewski Krzysztof
Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
Department of Chemistry, Case Western Reserve University, Cleveland, Ohio, USA.
Nat Chem Biol. 2015 Jun;11(6):409-15. doi: 10.1038/nchembio.1799. Epub 2015 Apr 20.
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.
脊椎动物的视觉功能依赖于膜结合类视黄醇异构酶RPE65，它是类视黄醇循环途径的一个重要组成部分，该途径为视杆和视锥视蛋白再生11-顺式视黄醛。由于类视黄醇如何结合到其活性位点尚不确定，RPE65催化立体选择性类视黄醇异构化的机制一直难以捉摸。在这里，我们展示了RPE65与类视黄醇模拟化合物复合物的晶体结构，其中一种化合物正在进行治疗年龄相关性黄斑变性的临床试验。这些结构揭示了位于酶的膜相互作用表面附近的活性位点类视黄醇结合腔，以及位于相邻口袋中的铁结合棕榈酸酯配体。随着RPE65-底物复合物的几何结构得以阐明，我们描述了一种催化机制，该机制与对该酶进行的广泛生化和结构研究相吻合。这些数据为理解视觉中的关键过程以及用小分子对RPE65进行药理学抑制提供了分子基础。
