Effect of glycation on α-crystallin structure and chaperone-like function
Effect of glycation on α-crystallin structure and chaperone-like function
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DOI：
10.1042/bj20070989
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发表时间：
2007-12-01
影响因子：
4.1
通讯作者：
Reddy, G. Bhanuprakash
中科院分区：
文献类型：
--
作者：
Kumar, P. Anil;Kumar, M. Satish;Reddy, G. Bhanuprakash
α-晶状体蛋白的分子伴侣样活性被认为在维持眼睛晶状体的透明度方面发挥重要作用。然而，在衰老和糖尿病的情况下，α-晶状体蛋白的伴侣功能受到损害，导致白内障的形成。一些翻译后修饰，包括非酶糖化，已被证明会影响 α-晶状体蛋白在衰老和糖尿病中的伴侣功能。多种物质已被确定为包括晶状体在内的各种组织中 AGE（晚期糖基化终产物）形成的主要来源。然而，α-晶状体蛋白与各种糖的糖化导致了不同的结果。在目前的体外研究中，我们研究了代表主要糖化剂类别的葡萄糖、果糖、G6P（6-磷酸葡萄糖）和MGO（甲基乙二醛）对α-晶状体蛋白的结构和伴侣功能的影响。使用所有四种试剂对 α-晶状体蛋白进行修饰会导致糖化蛋白的形成、AGE 荧光增加、蛋白交联和 HMM（高分子质量）聚集。有趣的是，这些糖化相关的情况被发现随着不同的糖化剂而变化。例如，CML [N-ε-(羧甲基)赖氨酸] 是 α-晶状体蛋白用这些药物糖化后形成的主要 AGE。虽然果糖和 MGO 引起显着的构象变化，但葡萄糖和 G6P 没有显着的结构扰动。除 MGO 修饰外，其他糖的糖化会导致聚集测定中的分子伴侣活性降低。然而，根据酶失活测定的评估，所有四种糖的修饰都会导致分子伴侣活性丧失。糖化诱导的α-晶状体蛋白伴侣活性丧失与疏水性降低相关。此外，从糖化 TSP（总晶状体可溶蛋白）中分离出的 α-晶状体蛋白也增加了 AGE 荧光、CML 形成并降低了伴侣活性。这些结果表明α-晶状体蛋白对各种糖及其衍生物的非酶糖化作用敏感，其水平在糖尿病中升高。我们还描述了糖化对 α-晶状体蛋白的结构和分子伴侣样活性的影响。
The chaperone-like activity of alpha-crystallin is considered to play an important role in the maintenance of the transparency of the eye lens. However, in the case of aging and in diabetes, the chaperone function of alpha-crystallin is compromized, resulting in cataract formation. Several post-translational modifications, including non-enzymatic glycation, have been shown to affect the chaperone function of alpha-crystallin in aging and in diabetes. A variety of agents have been identified as the predominant sources for the formation of AGEs (advanced glycation end-products) in various tissues, including the lens. Nevertheless, glycation of alpha-crystallin with various sugars has resulted in divergent results. In the present in vitro study, we have investigated the effect of glucose, fructose, G6P (glucose 6-phosphate) and MGO (methylglyoxal), which represent the major classes of glycating agents, on the structure and chaperone function of alpha-crystallin. Modification of alpha-crystallin with all four agents resulted in the formation of glycated protein, increased AGE fluorescence, protein cross-linking and HMM (high-molecular-mass) aggregation. Interestingly, these glycation-related profiles were found to vary with different glycating agents. For instance, CML [N-epsilon-(carboxymethyl)lysine] was the predominant AGE formed upon glycation of alpha-crystallin with these agents. Although fructose and MGO caused significant conformational changes, there were no significant structural perturbations with glucose and G6P. With the exception of MGO modification, glycation with other sugars resulted in decreased chaperone activity in aggregation assays. However, modification with all four sugars led to the loss of chaperone activity as assessed using an enzyme inactivation assay. Glycation-induced loss of alpha-crystallin chaperone activity was associated with decreased hydrophobicity. Furthermore, alpha-crystallin isolated from glycated TSP (total lens soluble protein) had also increased AGE fluorescence, CML formation and diminished chaperone activity. These results indicate the susceptibility of alpha-crystallin to non-enzymatic glycation by various sugars and their derivatives, whose levels are elevated in diabetes. We also describes the effects of glycation on the structure and chaperone-like activity of alpha-crystallin.