Ramon Eva, Cordomí Arnau, Aguilà Mònica, Srinivasan Sundaramoorthy, Dong Xiaoyun, Moore Anthony T, Webster Andrew R, Cheetham Michael E, Garriga Pere
From the Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Rambla de Sant Nebridi 22, 08222 Terrassa, Spain.
the Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain.
J Biol Chem. 2014 Dec 26;289(52):35918-28. doi: 10.1074/jbc.M114.609958. Epub 2014 Oct 30.
Retinitis pigmentosa (RP) is a group of genetically and clinically heterogeneous inherited degenerative retinopathies caused by abnormalities of photoreceptors or retinal pigment epithelium in the retina leading to progressive sight loss. Rhodopsin is the prototypical G-protein-coupled receptor located in the vertebrate retina and is responsible for dim light vision. Here, novel M39R and N55K variants were identified as causing an intriguing sector phenotype of RP in affected patients, with selective degeneration in the inferior retina. To gain insights into the molecular aspects associated with this sector RP phenotype, whose molecular mechanism remains elusive, the mutations were constructed by site-directed mutagenesis, expressed in heterologous systems, and studied by biochemical, spectroscopic, and functional assays. M39R and N55K opsins had variable degrees of chromophore regeneration when compared with WT opsin but showed no gross structural misfolding or altered trafficking. M39R showed a faster rate for transducin activation than WT rhodopsin with a faster metarhodopsinII decay, whereas N55K presented a reduced activation rate and an altered photobleaching pattern. N55K also showed an altered retinal release from the opsin binding pocket upon light exposure, affecting its optimal functional response. Our data suggest that these sector RP mutations cause different protein phenotypes that may be related to their different clinical progression. Overall, these findings illuminate the molecular mechanisms of sector RP associated with rhodopsin mutations.
视网膜色素变性（RP）是一组由视网膜中光感受器或视网膜色素上皮异常引起的遗传性退行性视网膜病变，具有遗传和临床异质性，可导致进行性视力丧失。视紫红质是位于脊椎动物视网膜中的典型G蛋白偶联受体，负责暗光视觉。在此，新型M39R和N55K变体被鉴定为导致受影响患者出现有趣的扇形RP表型，表现为视网膜下部选择性变性。为了深入了解与这种扇形RP表型相关的分子机制（其分子机制仍然难以捉摸），通过定点诱变构建突变体，在异源系统中表达，并通过生化、光谱和功能分析进行研究。与野生型视蛋白相比，M39R和N55K视蛋白具有不同程度的发色团再生，但未显示出明显的结构错误折叠或转运改变。M39R比野生型视紫红质具有更快的转导素激活速率，且视紫红质II衰变更快，而N55K则表现出激活速率降低和光漂白模式改变。N55K在光照下还显示出视蛋白结合口袋中视网膜释放的改变，影响其最佳功能反应。我们的数据表明，这些扇形RP突变导致不同的蛋白质表型，这可能与其不同的临床进展有关。总体而言，这些发现阐明了与视紫红质突变相关的扇形RP的分子机制。
