IMAGING ACTIVITY IN VISUAL CORTEX AT THE CELLULAR LEVEL

Tubby样蛋白（TULP）包括在所有多细胞生物中发现的蛋白质家族。 这些分子的特征在于存在保守的羧基末端“tubby结构域”，其不表现出与其他已知蛋白质的序列同源性。tubby或其他TULP的基因突变通常导致三种疾病表型中的一种或多种：（1）肥胖-“tubby”的名称来源于此，（2）视网膜变性，和（3）听力损失。 与tubby样蛋白突变相关的疾病表型清楚地表明了这些分子在正常组织功能中的重要作用。虽然每个家族成员的表达模式各不相同，但tubby蛋白主要存在于神经系统中，并且所有已知的人类tubby蛋白都在视网膜中表达。 TULP 1基因的突变是14型视网膜色素变性的原因（约占遗传性RP病例的5%），而人类TULP 2基因在19号染色体上锥-杆视网膜营养不良基因座的最小识别区域内定位。此外，tubby突变体与几种导致感音神经性听力损失和视网膜退化并伴有肥胖的人类综合征具有显著的相似性。尽管tubby样蛋白的医学重要性明确，但尚未将生化功能归因于该蛋白质家族的任何成员。 为了确定tubby和其他TULP的生化功能-从而了解它们在疾病中的作用-我们将使用X射线晶体学来确定tubby的高分辨率三维结构。 我们将根据与其他已知蛋白质的结构相似性，通过鉴定化学功能（如活性位点或辅因子），以及通过应用伴随的细胞生物学和生化研究（包括细胞和亚细胞定位研究），确定tubby的功能。 这是一个模型问题的“结构基因组学”的方法，以确定功能的医学相关蛋白质。 这种方法依赖于结构信息，表型数据，和经典的生物学方法，使纯蛋白质的可用性。 这种类型的方法应该大大促进了最近的大规模扩展的三维结构的数据库。

Tubby-like proteins (TULPs) comprise a family of proteins found in all multicellular organisms. These molecules are characterized by the presence of a conserved carboxy-terminal "tubby domain" that does not exhibit sequence homology to other known proteins. Genetic mutation of tubby or other TULPs often leads to one or more of three disease phenotypes: (1) obesity - from which the name "tubby" is derived, (2) retinal degeneration, and (3) hearing loss. The disease phenotypes associated with mutations in tubby-like proteins clearly indicate a vital role for these molecules in normal tissue function. While the expression pattern of each family member is distinctive, tubby proteins are found mainly in the nervous system, and all known human tubby proteins are expressed in the retina. Mutation of the TULP1 gene is the cause of retinitis pigmentosa type 14 (about 5 percent of inherited RP cases), and the human TULP2 gene maps within the minimal identified region for the cone-rod retinal dystrophy locus on chromosome 19. Furthermore, tubby mutants bear a remarkable similarity to several human syndromes that result in combined sensorineural hearing loss and retinal degradation, accompanied by obesity. Despite the clear medical importance of tubby-like proteins, no biochemical function has yet been ascribed to any member of this protein family. In order to identify the biochemical function of tubby and other TULPs -and to thus understand their role in disease - we will use X-ray crystallography to determine the high-resolution three-dimensional structure of tubby. We will identify a function for tubby based on structural similarities to other known proteins, by identification of chemical functionalities such as active sites or cofactors, and by the application of concomitant cell biological and biochemical studies, including cellular and sub-cellular localization studies. This is a model problem for a "structural genomics" approach to identification of function for a medically relevant protein. This approach relies on structural information, phenotype data, and classical biology approaches enabled by the availability of pure protein. This type of approach should be greatly facilitated by the recent massive expansion of the database of three-dimensional structures.