Rao Yan, Dong Sufang, Li Zuhua, Yang Guohua, Peng Chunyan, Yan Ming, Zheng Fang
Center for Gene Diagnosis, Zhongnan Hospital of Wuhan University, Wuhan, China.
Department of Medical Genetics, School of Basic Medical Science, Wuhan University, Wuhan, China.
Mol Vis. 2017 Sep 1;23:624-637. eCollection 2017.
To identify the potential candidate genes for a large Chinese family with autosomal dominant congenital cataract (ADCC) and nystagmus, and investigate the possible molecular mechanism underlying the role of the candidate genes in cataractogenesis.
We combined the linkage analysis and direct sequencing for the candidate genes in the linkage regions to identify the causative mutation. The molecular and bio-functional properties of the proteins encoded by the candidate genes was further explored with biophysical and biochemical studies of the recombinant wild-type and mutant proteins.
We identified a c. C749T (p.Q227X) transversion in exon 6 of , a cataract-causative gene. This nonsense mutation changes a phylogenetically conserved glutamine to a stop codon and is predicted to truncate the C-terminus of the wild-type protein by 26 amino acids. Comparison of the biophysical and biochemical properties of the recombinant full-length and truncated βB1-crystallins revealed that the mutation led to the insolubility and the phase separation phenomenon of the truncated protein with a changed conformation. Meanwhile, the thermal stability of the truncated βB1-crystallin was significantly decreased, and the mutation diminished the chaperoning ability of αA-crystallin with the mutant under heating stress.
Our findings highlight the importance of the C-terminus in βB1-crystallin in maintaining the crystalline function and stability, and provide a novel insight into the molecular mechanism underlying the pathogenesis of human autosomal dominant congenital cataract.
鉴定一个患有常染色体显性遗传性先天性白内障（ADCC）和眼球震颤的中国大家庭的潜在候选基因，并研究候选基因在白内障发生过程中发挥作用的可能分子机制。
我们将连锁分析与连锁区域内候选基因的直接测序相结合，以鉴定致病突变。通过对重组野生型和突变型蛋白质进行生物物理和生化研究，进一步探索候选基因编码蛋白质的分子和生物功能特性。
我们在一个白内障致病基因的第6外显子中鉴定出一个c.C749T（p.Q227X）颠换。这种无义突变将一个系统发育保守的谷氨酰胺改变为一个终止密码子，并预计使野生型蛋白质的C末端截短26个氨基酸。对重组全长和截短的βB1-晶体蛋白的生物物理和生化特性进行比较后发现，该突变导致截短蛋白出现不溶性和相分离现象，且其构象发生改变。同时，截短的βB1-晶体蛋白的热稳定性显著降低，并且该突变削弱了αA-晶体蛋白在热应激下对突变体的伴侣功能。
我们的研究结果突出了βB1-晶体蛋白C末端在维持晶状体功能和稳定性方面的重要性，并为人类常染色体显性遗传性先天性白内障发病机制的分子机制提供了新的见解。
