Congenital microcornea-cataract syndrome-causing mutation X253R increases βB1-crystallin hydrophobicity to promote aggregate formation
Congenital microcornea-cataract syndrome-causing mutation X253R increases βB1-crystallin hydrophobicity to promote aggregate formation
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DOI：
10.1042/bcj20160247
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发表时间：
2016-07-01
影响因子：
4.1
通讯作者：
Yan, Yong-Bin
中科院分区：
文献类型：
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作者：
Leng, Xiao-Yao;Li, Hai-Yun;Yan, Yong-Bin
晶状体蛋白的高溶解度和终生稳定性对于维持晶状体透明度和光学性能至关重要。许多晶状体蛋白突变与先天性白内障有关，这是新生儿失明的主要原因之一。除了白内障之外，一些晶状体蛋白突变也与先天性小角膜白内障综合征（CMCC）等综合征有关。然而，晶状体蛋白突变引起CMCC的分子机制仍不清楚。在本研究中，我们研究了β B1-晶状体蛋白X253R突变引起CMCC的机制。外源表达的X253R蛋白在HeLa细胞中易于形成p62阴性聚集体，强烈抑制细胞增殖并诱导细胞凋亡。细胞内的 X253R 聚集体可以被羊毛甾醇成功地重新溶解，但不能被胆固醇重新溶解。 X253R突变引入的βB1-晶状体蛋白C端额外的26个残基对βB1-晶状体蛋白结构和稳定性影响不大，但增加了βB1-晶状体蛋白的疏水性并降低了其溶解度。有趣的是，X253R突变体完全消除了βB1-和βA3/βB1-晶状体蛋白在高温下的聚集倾向，这表明X253R是β-晶状体蛋白同聚物和异聚物在稀溶液中的聚集抑制突变。我们的结果表明，疏水性的增加和溶解度的降低可能是 X253R 突变诱导的白内障发生的原因，而 X253R 聚集体的细胞毒性作用可能导致眼睛发育缺陷。我们的结果还强调，至少在某些情况下，稀溶液中的聚集倾向不能完全模拟细胞拥挤的细胞质中突变蛋白质的行为。
The high solubility and lifelong stability of crystallins are crucial to the maintenance of lens transparency and optical properties. Numerous crystallin mutations have been linked to congenital cataract, which is one of the leading causes of newborn blindness. Besides cataract, several crystallin mutations have also been linked to syndromes such as congenital microcornea-cataract syndrome (CMCC). However, the molecular mechanism of CMCC caused by crystallin mutations remains elusive. In the present study, we investigated the mechanism of CMCC caused by the X253R mutation in beta B1-crystallin. The exogenously expressed X253R proteins were prone to form p62-negative aggregates in HeLa cells, strongly inhibited cell proliferation and induced cell apoptosis. The intracellular X253R aggregates could be successfully redissolved by lanosterol but not cholesterol. The extra 26 residues at the C-terminus of beta B1-crystallin introduced by the X253R mutation had little impact on beta B1-crystallin structure and stability, but increased beta B1-crystallin hydrophobicity and decreased its solubility. Interestingly, the X253R mutant fully abolished the aggregatory propensity of beta B1- and beta A3/beta B1-crystallins at high temperatures, suggesting that X253R was an aggregation-inhibition mutation of beta-crystallin homomers and heteromers in dilute solutions. Our results suggest that an increase in hydrophobicity and a decrease in solubility might be responsible for cataractogenesis induced by the X253R mutation, while the cytotoxic effect of X253R aggregates might contribute to the defects in ocular development. Our results also highlight that, at least in some cases, the aggregatory propensity in dilute solutions could not fully mimic the behaviours of mutated proteins in the crowded cytoplasm of the cells.