Modifications of Small Heat Shock Proteins in the Lens

在透镜中发现的两种小的热休克蛋白（Hsps）α-晶状体蛋白和热休克蛋白27（Hsp 27）被认为保护透镜蛋白免受诸如氧化和紫外线的应激。除了作为伴侣蛋白的功能外，它们还是多功能的抗凋亡蛋白。在透镜中，丙酮醛（MGO）是糖酵解过程中产生的代谢副产物，其浓度至少是血浆中的20倍。来自糖尿病患者的镜片具有比来自非糖尿病个体的镜片高得多的MGO浓度。MGO易于与蛋白质中的赖氨酸、精氨酸和半胱氨酸残基反应以形成稳定的加合物，其中几种已在人透镜中鉴定。我们最近对MGO修饰的研究提供了令人惊讶的结果，即MGO修饰增强了sHsps的伴侣功能。我们最近的研究表明，白内障晶状体含有高水平的磷酸化Hsp 27（pHsp 27）和pHsp 27是高度敏感的修改MGO。我们还发现MGO修饰的α-晶状体蛋白是比天然未修饰蛋白更好的抗凋亡蛋白。这些有趣的观察结果促使我们进一步研究MGO诱导的sHsps结构改变，并确定这些改变如何改变它们的功能。我们有四个目标。在目标1中，我们将详细研究sHsps暴露于MGO所导致的结构变化。我们将重点关注精氨酸残基，因为这些残基最容易被MGO修饰。在目标2中，我们将确定MGO诱导的修饰如何改变sHsps的抗凋亡功能。在目标3中，我们将研究MGO诱导的修饰对sHsps与其他透镜蛋白相互作用的影响。最后，在目标4中，我们将确定在增加的细胞应激期间sHsps的MGO修饰是否影响它们向细胞核的运输。这些研究将提高我们对sHsps和代谢途径之间相互作用的理解，它们将帮助我们确定sHsps在透镜上皮细胞凋亡中的作用以及对白内障形成的影响。

Alpha-crystallin and heat shock protein-27 (Hsp27), the two small heat shock proteins (Hsps) found in the lens are thought to protect lens proteins from the stress, such as, oxidation and ultra violet light. In addition to functioning as chaperone proteins, they are versatile anti-apoptotic proteins. In the lens methylglyoxal (MGO) is produced as a metabolic by-product during glycolysis and its concentration is at least 20 times higher than in plasma. Lenses from diabetics have far greater MGO concentrations than lenses from nondiabetic individuals. MGO readily reacts with lysine, arginine and cysteine residues in proteins to form stable adducts, several of which have been identified in the human lens. Our recent studies on MGO modifications provided the surprising results that MGO-modification enhances the chaperone function of sHsps. Our most recent studies demonstrate that cataractous lenses contain high levels of phosphorylated Hsp27 (pHsp27) and pHsp27 is highly susceptible for modification by MGO. We also found MGO-modified alpha-crystallin is a better anti-apoptotic protein than the native unmodified protein. These intriguing observations prompted us to examine further on the MGO-induced structural alterations in sHsps, and to determine how such alterations change their functions. We have four aims. In aim 1, we will examine in detail the structural changes resulting from exposure of sHsps to MGO. We will focus on arginine residues, because these are the most vulnerable to modification by MGO. In aim 2, we will determine how MGO-induced modifications alter the anti-apoptotic functions of sHsps. In aim 3, we will study the impact of MGO-induced modifications on the interaction of sHsps with other lens proteins. Finally, in aim 4, we will determine whether MGO-modification of sHsps influence their transportation into the nucleus during increased cellular stress. These studies will improve our understanding of the interplay between sHsps and metabolic pathways, and they will help us to define the role of sHsps in apoptosis of lens epithelial cells and the implications for cataract formation.