Yu Dongmei, Zou Junhuang, Chen Qian, Zhu Tian, Sui Ruifang, Yang Jun
Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, Salt Lake City, UT, United States.
Department of Ophthalmology, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China.
Comput Struct Biotechnol J. 2020 Jun 10;18:1363-1382. doi: 10.1016/j.csbj.2020.05.025. eCollection 2020.
Usherin is the most common causative protein associated with autosomal recessive retinitis pigmentosa (RP) and Usher syndrome (USH), which are characterized by retinal degeneration alone and in combination with hearing loss, respectively. Usherin is essential for photoreceptor survival and hair cell bundle integrity. However, the molecular mechanism underlying usherin function in normal and disease conditions is unclear. In this study, we investigated structural models of usherin domains and localization of usherin pathogenic small in-frame mutations, mainly homozygous missense mutations. We found that usherin fibronectin III (FN3) domains and most laminin-related domains have a β-sandwich structure. Some FN3 domains are predicted to interact with each other and with laminin-related domains. The usherin protein may bend at some FN3 linker regions. RP- and USH-associated small in-frame mutations are differentially located in usherin domains. Most of them are located at the periphery of β-sandwiches, with some at the interface between interacting domains. The usherin laminin epidermal growth factor repeats adopt a rod-shaped structure, which is maintained by disulfide bonds. Most missense mutations and deletion of exon 13 in this region disrupt the disulfide bonds and may affect local protein folding. Despite low expression of the recombinant entire protein and protein fragments in mammalian cell culture, usherin FN3 fragments are more robustly expressed and secreted than its laminin-related fragments. Our findings provide new insights into the usherin structure and the disease mechanisms caused by pathogenic small in-frame mutations, which will help inform future experimental research on diagnosis, disease mechanisms, and therapeutic approaches.
usherin是与常染色体隐性视网膜色素变性（RP）和Usher综合征（USH）相关的最常见致病蛋白，RP单独以视网膜变性为特征，USH则伴有听力丧失。usherin对光感受器存活和毛细胞束完整性至关重要。然而，usherin在正常和疾病状态下起作用的分子机制尚不清楚。在本研究中，我们研究了usherin结构域的结构模型以及usherin致病性框内小突变（主要是纯合错义突变）的定位。我们发现usherin纤连蛋白III（FN3）结构域和大多数层粘连蛋白相关结构域具有β-折叠结构。一些FN3结构域预计会相互作用，并与层粘连蛋白相关结构域相互作用。usherin蛋白可能在一些FN3连接区域发生弯曲。与RP和USH相关的框内小突变在usherin结构域中的定位不同。它们大多位于β-折叠的外围，有些位于相互作用结构域之间的界面处。usherin层粘连蛋白表皮生长因子重复序列采用杆状结构，由二硫键维持。该区域的大多数错义突变和外显子13缺失会破坏二硫键，并可能影响局部蛋白质折叠。尽管重组全长蛋白和蛋白片段在哺乳动物细胞培养中的表达水平较低，但usherin FN3片段的表达和分泌比其层粘连蛋白相关片段更稳定。我们的研究结果为usherin结构以及致病性框内小突变引起的疾病机制提供了新的见解，这将有助于为未来关于诊断、疾病机制和治疗方法的实验研究提供信息。
