Singhal Ankita, Guo Ying, Matkovic Milos, Schertler Gebhard, Deupi Xavier, Yan Elsa Cy, Standfuss Joerg
Division of Biology and Chemistry, Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen, Switzerland.
Department of Chemistry, Yale University, New Haven, CT, USA.
EMBO Rep. 2016 Oct;17(10):1431-1440. doi: 10.15252/embr.201642671. Epub 2016 Jul 25.
Congenital stationary night blindness (CSNB) is an inherited and non-progressive retinal dysfunction. Here, we present the crystal structure of CSNB-causing T94I rhodopsin in the active conformation at 2.3 Å resolution. The introduced hydrophobic side chain prolongs the lifetime of the G protein activating metarhodopsin-II state by establishing a direct van der Waals contact with K296, the site of retinal attachment. This is in stark contrast to the light-activated state of the CSNB-causing G90D mutation, where the charged mutation forms a salt bridge with K296 To find the common denominator between these two functional modifications, we combined our structural data with a kinetic biochemical analysis and molecular dynamics simulations. Our results indicate that both the charged G90D and the hydrophobic T94I mutation alter the dark state by weakening the interaction between the Schiff base (SB) and its counterion E113 We propose that this interference with the tight regulation of the dim light photoreceptor rhodopsin increases background noise in the visual system and causes the loss of night vision characteristic for CSNB patients.
先天性静止性夜盲症（CSNB）是一种遗传性且非进行性的视网膜功能障碍。在此，我们展示了导致CSNB的T94I视紫红质处于活性构象时2.3埃分辨率的晶体结构。引入的疏水侧链通过与视网膜附着位点K296建立直接的范德华接触，延长了激活G蛋白的视紫红质II状态的寿命。这与导致CSNB的G90D突变的光激活状态形成鲜明对比，在G90D突变中，带电突变与K296形成盐桥。为了找到这两种功能修饰之间的共同特征，我们将结构数据与动力学生化分析及分子动力学模拟相结合。我们的结果表明，带电的G90D和疏水的T94I突变均通过削弱席夫碱（SB）与其抗衡离子E113之间的相互作用来改变暗态。我们提出，这种对视紫红质暗光感受器紧密调节的干扰会增加视觉系统中的背景噪声，并导致CSNB患者出现夜盲特征。
