Lesch-Nyhan disease: dissecting the functions of HGprt

描述（申请人提供）：莱施-尼汉病（LND）是一种神经遗传性疾病，以高尿酸血症和特征性神经行为综合征为特征。与大多数其他神经遗传性疾病一样，LND的发病机制反映了一个多步骤的过程，从原发性遗传缺陷，通过继发性生化变化，然后是最终导致临床表型的三级生理和解剖学变化。LND是由编码次黄嘌呤-鸟嘌呤磷酸核糖基转移酶（HGprt）的基因突变引起的，HGprt是一种在嘌呤代谢中发挥良好作用的酶。具体而言，它在补救途径中具有双重功能，用于回收次黄嘌呤和鸟嘌呤。虽然HGprt酶活性的丧失是主要的生化缺陷，但也已确定了多个额外的继发性生化变化。目前，我们对这些生化变化中哪些与病理生理级联中的下游事件最相关以及这些变化如何产生神经行为综合征的理解非常有限。本研究旨在分离HGprt的两种功能，次黄嘌呤再循环（Hprt）和鸟嘌呤再循环（Gprt），以确定哪一种在发病机制中最重要。我们的工作假设是，临床表型的发病机制主要取决于1或其他功能。AIM 1致力于对与人类疾病相关的HGprt突变的大型数据库进行计算机图形建模，以预测可能是次黄嘌呤或鸟嘌呤的选择性再循环的临床相关突变体。AIM 2致力于通过AIM 1中鉴定的信息突变体的直接生物化学测定对计算机图形建模的结果进行经验验证。这些实验的结果将提供一个重大的进步，我们的理解的发病机制的神经行为特征的LND通过确定HGPRT的2个主要的生化功能是最相关的发病机制。结果的意义并不限于LND，因为计算机图形建模的这种新应用也可用于阐明与具有多种底物的蛋白质相关的其他疾病或配体-蛋白质相互作用与临床表型之间的关系尚未很好理解的疾病的发病机制中的关键步骤。

DESCRIPTION (provided by applicant): Lesch-Nyhan disease (LND) is a neurogenetic disorder characterized by hyperuricemia and a characteristic neurobehavioral syndrome. Like most other neurogenetic diseases, the pathogenesis of LND reflects a multi- step process leading from the primary genetic defect, through secondary biochemical changes, and then tertiary physiologic and anatomical changes which ultimately lead to the clinical phenotype. LND is caused by mutations in the gene encoding hypoxanthine-guanine phosphoribosyltransferase (HGprt), an enzyme that plays a well-characterized role in purine metabolism. Specifically, it has dual functions in the salvage pathways, serving to recycle both hypoxanthine and guanine. Although the loss of HGprt enzyme activity is the primary biochemical defect, multiple additional secondary biochemical changes have also been identified. Currently, we have a very limited understanding of which of these biochemical changes is most relevant to downstream events in the pathophysiological cascade and how these changes produce the neurobehavioral syndrome. The studies of this proposal are aimed at separating the 2 functions of HGprt, hypoxanthine recycling (Hprt) and guanine recycling (Gprt), to determine which is most important for pathogenesis. Our working hypothesis is that the pathogenesis of the clinical phenotype depends predominantly on 1 or the other function. AIM 1 is devoted to computer graphic modeling of a large database of HGprt mutations associated with human disease to predict clinically relevant mutants that may be selective recyclers of hypoxanthine or guanine. AIM 2 is devoted to empirical verification of the results of computer graphic modeling via direct biochemical assay of the informative mutants identified in AIM 1. The results of these experiments will provide a major advance in our understanding of the pathogenesis of the neurobehavioral features of LND by determining which of the 2 main biochemical functions of HGprt is most relevant for pathogenesis. The significance of the results is not limited to LND, as this novel application of computer graphic modeling could also be used to elucidate key steps in the pathogenesis of other disorders associated with proteins that have multiple substrates or disorders where the relationship between ligand-protein interactions and clinical phenotype is not well understood.