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Abstract：
Despite of increasingly accumulated genetic variations of autosomal dominant congenital cataracts (ADCC), the causative genes of many ADCC patients remains unknown. In this research, we identified a novel F30S mutation in γS-crystallin from a three-generation Chinese family with ADCC. The patients possessing the F30S mutation exhibited nuclear cataract phenotype. The potential molecular mechanism underlying ADCC by the F30S mutation was investigated by comparing the structural features, stability and aggregatory potency of the mutated protein with the wild type protein. Spectroscopic experiments indicated that the F30S mutation did not affect γS-crystallin secondary structure compositions, but modified the microenvironments around aromatic side-chains. Thermal and chemical denaturation studies indicated that the mutation destabilized the protein and increased its aggregatory potency. The mutation altered the two-state unfolding of γS-crystallin to a three-state unfolding with the accumulation of an unfolding intermediate. The almost identical values in the changes of Gibbs free energies for transitions from the native state to intermediate and from the intermediate to unfolded state suggested that the mutation probably disrupted the cooperativity between the two domains during unfolding. Our results expand the genetic variation map of ADCC and provide novel insights into the molecular mechanism underlying ADCC caused by mutations in β/γ-crystallins.
摘要：
尽管常染色体显性先天性白内障（ADCC）的遗传变异越来越多，许多ADCC患者的致病基因仍然未知.在这项研究中,我们从一个具有ADCC的中国三代家族中鉴定出γS-晶状体蛋白中的新F30S突变。具有F30S突变的患者表现为核性白内障表型。通过比较F30S突变的潜在分子机制研究了ADCC的结构特征，突变蛋白与野生型蛋白的稳定性和聚集能力。光谱实验表明，F30S突变不影响γS-晶状体蛋白二级结构组成，但改变了芳香侧链周围的微环境。热和化学变性研究表明，突变使蛋白质不稳定，并增加了其聚集能力。突变将γS-晶状体蛋白的两状态解折叠改变为三状态解折叠，并积累了解折叠中间体。从天然状态到中间状态以及从中间状态到展开状态的吉布斯自由能变化几乎相同的值表明，突变可能会破坏展开过程中两个域之间的协同性。我们的结果扩展了ADCC的遗传变异图谱，并为β/γ-晶状体蛋白突变引起的ADCC的分子机制提供了新的见解。
