Yan Hong, Harding John J
Nuffield Laboratory of Ophthalmology, University of Oxford, Walton St., Oxford OX2 6AW, UK.
Biol Chem. 2003 Aug;384(8):1185-94. doi: 10.1515/BC.2003.131.
Previously we showed that glycation-induced inactivation and loss of antigenicity of enzymes occur simultaneously. Alpha-crystallin, a major structural protein of the mammalian lens, prevents the aggregation of other proteins and protects enzyme function against post-translational modification in vitro. However, it is not known whether alpha-crystallin can also protect against loss of antigenicity of enzymes. Esterase activity in the lens is decreased in senile cataract and diabetes. We investigated the loss of antigenicity of esterase caused by different insults and the ability of alpha-crystallin to protect. Inactivation of carboxylesterase by sugars, fructose 6-phosphate (F6P) and a steroid, prednisolone-21-hemisuccinate (P-21-H), was measured spectrophotometrically in the presence and absence of alpha-crystallin, while loss of antigenicity was monitored simultaneously using an immunoprecipitation method. The esterase was progressively inactivated by fructose, F6P, ribose, and P-21-H. Bovine alpha-crystallin fully protected against inactivation of esterase by all four compounds, and also protected against loss of antigenicity of the esterase by fructose, ribose and P-21-H at a molar ratio of 1:1. The results indicated that alpha-crystallin, under our experimental conditions, clearly exhibited the ability to prevent loss of antigenicity and inactivation of esterase. The protective effect of alpha-crystallin against loss of antigenicity indicates a novel aspect of its chaperoning function.
此前我们发现，糖基化诱导的酶失活和抗原性丧失是同时发生的。α-晶状体蛋白是哺乳动物晶状体的主要结构蛋白，它能防止其他蛋白质聚集，并在体外保护酶功能免受翻译后修饰的影响。然而，尚不清楚α-晶状体蛋白是否也能防止酶的抗原性丧失。在老年性白内障和糖尿病中，晶状体中的酯酶活性会降低。我们研究了不同损伤导致的酯酶抗原性丧失以及α-晶状体蛋白的保护能力。在有和没有α-晶状体蛋白存在的情况下，通过分光光度法测定糖、6-磷酸果糖（F6P）和一种类固醇泼尼松龙-21-半琥珀酸酯（P-21-H）对羧酸酯酶的失活作用，同时使用免疫沉淀法监测抗原性丧失情况。酯酶被果糖、F6P、核糖和P-21-H逐渐失活。牛α-晶状体蛋白能完全保护酯酶不被这四种化合物失活，并且在摩尔比为1:1时，还能保护酯酶不被果糖、核糖和P-21-H丧失抗原性。结果表明，在我们的实验条件下，α-晶状体蛋白明显表现出防止酯酶抗原性丧失和失活的能力。α-晶状体蛋白对抗原性丧失的保护作用表明了其伴侣功能的一个新方面。
