Racemization of Two Proteins over Our Lifespan: Deamidation of Asparagine 76 in γS Crystallin Is Greater in Cataract than in Normal Lenses across the Age Range
Racemization of Two Proteins over Our Lifespan: Deamidation of Asparagine 76 in γS Crystallin Is Greater in Cataract than in Normal Lenses across the Age Range
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DOI：
10.1167/iovs.11-9085
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发表时间：
2012-06-01
影响因子：
4.4
通讯作者：
Truscott, Roger John Willis
中科院分区：
文献类型：
--
作者：
Hooi, Michelle Yu Sung;Raftery, Mark J.;Truscott, Roger John Willis
目的.长寿蛋白在人类中广泛存在，但对随着时间的推移影响其功能的过程或其在年龄相关疾病中的作用知之甚少。使用胰蛋白酶消化和LC/质谱法比较了来自正常和白内障人晶状体的两种蛋白质的外消旋与年龄的关系。研究了α A晶体蛋白中的Asp 151和γ S晶体蛋白中的Asn 76。正常晶状体中两种蛋白质的蛋白质依赖性谱是不同的。在这两种蛋白质中，修饰都没有随着年龄的增长而线性增加。对于α A晶体蛋白，外消旋化在生命的前15年发生得最快，大约一半的L-Asp 151转化为D-isoAsp、L-isoAsp和D-Asp，比例为3：1：0.5。此后，价值观变化不大。相比之下，γ S晶状体蛋白中Asn 76的外消旋化缓慢，直到15岁，isoAsp仅占5%。值保持相对恒定，直到40岁时发生线性增长（1%/年）。当白内障晶状体与年龄匹配的正常晶状体相比时，两种晶状体蛋白的时间过程存在显著差异。对于α A晶体蛋白，白内障和正常晶状体之间的Asp 151消旋化没有显著差异。相比之下，在γ S晶体蛋白中，在白内障晶状体中Asn 76转化为isoAsp的程度在每个年龄段都是正常人的大约两倍。Asn和Asp随时间的修饰可能导致人透镜中蛋白质的变性。蛋白质（例如γ S晶状体蛋白）中选定位点的脱酰胺/外消旋速率加快可能会导致白内障形成。（Invest Ophthalmol维斯科学。2012;53：3554-3561）DOI：10.1167/iovs.11-9085
PURPOSE. Long-lived proteins are widespread in man, yet little is known about the processes that affect their function over time, or their role in age-related diseases.METHODS. Racemization of two proteins from normal and cataract human lenses were compared with age using tryptic digestion and LC/mass spectrometry. Asp 151 in alpha A crystallin and Asn 76 in gamma S crystallin were studied.RESULTS. Age-dependent profiles for the two proteins from normal lenses were different. In neither protein did the modifications increase linearly with age. For alpha A crystallin, racemization occurred most rapidly during the first 15 years of life, with approximately half of L-Asp 151 converted to D-isoAsp, L-isoAsp, and D-Asp in a ratio of 3:1:0.5. Values then changed little. By contrast, racemization of Asn 76 in gamma S crystallin was slow until age 15, with isoAsp accounting for only 5%. Values remained relatively constant until age 40 when a linear increase (1%/year) took place. When cataract lenses were compared with age-matched normal lenses, there were marked differences in the time courses of the two crystallins. For alpha A crystallin, there was no significant difference in Asp 151 racemization between cataract and normal lenses. By contrast, in gamma S crystallin the degree of conversion of Asn 76 to isoAsp in cataract lenses was approximately double that of normals at every age.CONCLUSIONS. Modification of Asn and Asp over time may contribute to denaturation of proteins in the human lens. An accelerated rate of deamidation/racemization at selected sites in proteins, such as gamma S crystallin, may contribute to cataract formation. (Invest Ophthalmol Vis Sci. 2012;53:3554-3561) DOI:10.1167/iovs.11-9085