Molecular Basis for Lens Transparency

描述（由申请人提供）：透镜老化的“磨损”通过其纤维细胞中晶体蛋白的累积修饰在分子水平上记录。在蛋白质周转不存在的情况下，这种缓慢的环境扰动导致晶状体蛋白稳定性和溶解度的逐渐丧失，并改变蛋白质-蛋白质相互作用，所有这些都损害了透镜的透明度和晶状体活性。纤维细胞重量的大约35%由分子伴侣，α-晶状体蛋白，一种结合聚集倾向蛋白的蛋白质稳定性传感器组成。α-晶体蛋白和不稳定的β-和β-之间的吸引力相互作用晶体蛋白是透镜老化的中心方面。分子伴侣能力的耗竭被假设为年龄相关性白内障的中心催化剂。此外，年龄相关性核性白内障的最早阶段与晶体蛋白的二硫键交联聚集体的出现在时间上相关。这项资助的长期目标是发展对晶体蛋白稳定性、伴侣结构、亲和力和能力以及透镜老化和白内障发展过程中分子拥挤之间相互关系的理解。在下一个资助期内，我们将测试两个关于年龄相关性和遗传性白内障分子机制的假设。目标1和2将对触发不稳定的？-和？-结合所需的能量阈值进行系统分析。晶体蛋白与α-晶体蛋白的相互作用，并确定分子伴侣驱动的相互作用是否通过复合物形成所提供的熵优势导致二硫键交联的形成。这项奋进的关键是使用一种创新的无标记方法，背散射干涉法，它允许这些相互作用的表征在真实的时间。我们还将从α-晶状体蛋白容量滴定和聚集体形成的角度检验与先天性白内障相关的α-晶状体蛋白半胱氨酸突变体导致压缩老化过程的假设。基于初步数据，这些突变体的复合物形成是由它们增加的亲和力和能力驱动的，而不是由底物不稳定驱动的，并导致形成二硫键交联。在目标3中，将采用现有技术的结构工具来提供分子伴侣激活状态及其与底物的复合物的快照。这些研究将通过识别参与结合的序列和结构基序，并通过小的热休克蛋白的寡聚体膨胀定义激活的基础，来补充目标1和2的机制见解。白内障形成是全世界失明的主要原因，在美国影响2000万成年人。在最常见的类型中，人类核性白内障、蛋白质聚集和二硫键交联是主要的分子事件。这些分子转化的机制观点的发展是基本的生物化学的重要性，很可能会对干预和治疗策略的发展产生影响。

DESCRIPTION (provided by applicant): The "wear and tear" of lens aging is recorded at the molecular level through accumulated modifications of the crystallins in its fiber cells. This slow environmental perturbation in the absence of protein turn-over leads to a progressive loss in crystallins stability and solubility and alters protein-protein interactions, all of which compromise lens transparency and refractivity. Roughly 35% of the fiber cell weight consists of the molecular chaperone, a-crystallin, a protein-stability sensor that binds aggregation-prone proteins. Attractive interactions between a-crystallin and destabilized ¿- and ?-crystallins are a central facet of lens aging. The exhaustion of chaperone capacity is hypothesized to be a central catalyst for age-related cataract. Furthermore, the earliest stage of age-related nuclear cataract is temporally correlated with the appearance of disulfide cross-linked aggregates of crystallins. The long term goal of this grant is to develop an understanding of the interrelationships between crystallins stability, chaperone structure, affinity and capacity, and molecular crowding in the process of lens aging and the development of cataract. In the next funding period, we will test two hypotheses regarding the molecular mechanisms of age-related and hereditary cataracts. Aims 1 and 2 will undertake a systematic analysis of the energetic threshold required to trigger binding of destabilized ¿- and ?-crystallins to a-crystallin and determine whether chaperone-driven interactions lead to formation of disulfide cross-links through the entropic advantage afforded by complex formation. Critical to this endeavor is the use of an innovative label-free approach, backscattering interferometry, which allows characterization of these interactions in real time. We will also test the hypothesis that A-crystallin cysteine mutants linked to congenital cataract lead to a compressed aging process from the perspective of titration of a-crystallin capacity and formation of aggregates. Based on preliminary data, complex formation by these mutants is driven by their increased affinity and capacity rather than by substrate destabilization and results in the formation of disulfide cross-links. In aim 3, state of the art structural tools will be employed to provide snapshots of a chaperone activated state and its complex with the substrate. These studies will complement the mechanistic insight of aims 1 and 2 by identifying sequence and structural motifs involved in binding, and defining the basis of activation by oligomer expansion of small heat-shock proteins. Cataract formation is a leading cause of blindness worldwide and affects 20 million adults in the United States. In the most common type, human nuclear cataract, protein aggregation and disulfide cross-linking are major molecular events. The development of a mechanistic perspective on these molecular transformations is of fundamental biochemical importance and may well have an impact on the development of intervention and therapeutic strategies.