The Children's Hospital, Zhejiang University School of Medicine, National Clinical Research Center for Child Health, Hangzhou 310052, China; Eye Center of the Second Affiliated Hospital, Zhejiang University School of Medicine, 88 Jiefang Road, Hangzhou 310009, China; Institute of Translational Medicine, Zhejiang University School of Medicine, 268 Kaixuan Road, Hangzhou 310020, China.
Eye Center of the Second Affiliated Hospital, Zhejiang University School of Medicine, 88 Jiefang Road, Hangzhou 310009, China.
Int J Biol Macromol. 2022 Jun 30;211:357-367. doi: 10.1016/j.ijbiomac.2022.04.205. Epub 2022 May 2.
Cataract is the most common pathogenic ophthalmic disease leading to blindness in children worldwide. Genetic disorder is the leading cause of congenital cataract, among which crystallin mutations have a high incidence. There are few reports on γA-crystallin, one critical member of crystallin superfamilies. In this study, we identified a novel pathogenic mutation (Ile82Met) in γA-crystallin from a three-generation Chinese family with cataract, and investigated the potential molecular mechanism in detail. To elucidate the pathogenic mechanism of I82M mutant, spectroscopic and solubility experiments were performed to determine the difference between the purified γA-crystallin wild type (WT) and I82M mutant under both physiological conditions and environmental stresses (UV irradiation, thermal denaturation or chemical denaturation). The I82M mutant did not affect the secondary/tertiary structure of monomeric γA-crystallin under physiological status, but decreased protein stability and increased aggregatory potency under the stressful treatment. Surprisingly, the chemical denaturation caused I82M to switch from the two-state unfolding of γA-crystallin to three-state unfolding involving an unfolding intermediate. This study expands the genetic variation map of cataract, and provides novel insights into the pathomechanism, in particular, filling in a gap in the understanding of γA-crystallin mutants causing cataract.
白内障是全球导致儿童失明的最常见眼病病因。遗传紊乱是先天性白内障的主要病因，其中晶状体突变的发病率较高。对于晶状体超家族的重要成员γA-晶状体蛋白，鲜有报道。在这项研究中，我们从一个三代中国白内障家系中鉴定出γA-晶状体蛋白的一个新的致病突变（Ile82Met），并详细研究了其潜在的分子机制。为阐明 I82M 突变体的致病机制，我们进行了光谱和溶解度实验，以确定在生理条件和环境应激（UV 照射、热变性或化学变性）下，纯化的野生型（WT）和 I82M 突变体γA-晶状体蛋白之间的差异。在生理状态下，I82M 突变不影响单体γA-晶状体蛋白的二级/三级结构，但在应激处理下降低了蛋白质稳定性并增加了聚集能力。令人惊讶的是，化学变性导致 I82M 从γA-晶状体蛋白的两态展开转变为涉及展开中间态的三态展开。本研究扩展了白内障的遗传变异图谱，并为其发病机制提供了新的见解，特别是填补了对导致白内障的γA-晶状体蛋白突变体的理解空白。
