Save Sight Institute, University of Sydney, Sydney, NSW, Australia.
Invest Ophthalmol Vis Sci. 2010 Jun;51(6):3107-14. doi: 10.1167/iovs.09-4308. Epub 2010 Jan 6.
Deamidation is a common posttranslational modification in human lens crystallins and may be a key factor in the age-related denaturation of such lifelong proteins. The aim of this study was to identify the sites of deamidation in older lenses.
High-performance liquid chromatography/mass spectrometry of tryptic digests was used to identify sites of deamidation in the major human lens crystallins. Older normal and age-matched cataractous lenses were compared with fetal lenses.
Approximately equal numbers of glutamine and asparagine residues were deamidated in older lenses; however, the extent of deamidation of Asn was three times greater than that of Gln (Asn, 22.6% +/- 3.6%; Gln, 6.6% +/- 1.3%). Individual crystallins differed markedly in their extent of deamidation, and deamidated residues were typically localized within discrete regions of the polypeptides. A large percentage (42%) of the sites of deamidation were characterized by the presence of a basic amino acid one residue removed from the original Gln or Asn. At nine such sites, the extent of Asn deamidation averaged 50% in aged lenses. There were few differences in deamidation between crystallins of aged normal and nuclear cataractous lenses.
Equal numbers of Asn and Gln residues are deamidated in crystallins from aged normal and cataractous lenses. Deamidation of Asn/Gln in lifelong proteins, such as those in the lens, may be governed to a significant degree by base-catalyzed processes.
脱酰胺作用是人类晶状体晶体蛋白的一种常见的翻译后修饰，可能是这些终生蛋白质与年龄相关的变性的关键因素。本研究的目的是确定在老年晶状体中脱酰胺的部位。
采用高效液相色谱/质谱联用技术对胰蛋白酶消化物进行分析，以鉴定主要人晶状体晶体蛋白中的脱酰胺部位。将老年正常晶状体和年龄匹配的白内障晶状体与胎晶状体进行比较。
在老年晶状体中，谷氨酰胺和天冬酰胺残基的脱酰胺数量大致相等；然而，天冬酰胺的脱酰胺程度是谷氨酰胺的三倍（天冬酰胺，22.6%±3.6%；谷氨酰胺，6.6%±1.3%）。个别晶体蛋白的脱酰胺程度差异显著，脱酰胺残基通常位于多肽的离散区域内。大量（42%）的脱酰胺部位的特征是在原始谷氨酰胺或天冬酰胺的一个残基处存在碱性氨基酸。在九个这样的位点中，老年晶状体中天冬酰胺脱酰胺的程度平均为 50%。在老年正常和核性白内障晶状体的晶体蛋白中，脱酰胺作用差异不大。
在老年正常和白内障晶状体的晶体蛋白中，天冬酰胺和谷氨酰胺残基的脱酰胺数量大致相等。在晶状体等终生蛋白质中天冬酰胺/谷氨酰胺的脱酰胺作用可能在很大程度上受到碱基催化过程的控制。
