Thrombospondin 4 A1

详细了解包括软骨低聚基质蛋白(COMP)在内的血栓反应蛋白(TSPs)在组织发生和修复过程中对细胞外基质(ECM)结构和细胞行为的调节作用是本研究的长期目标。下一个支助期的具体重点将放在以下领域。具体目的1.确定COMP与蛋白质和蛋白多糖(PG)相互作用的关键氨基酸。我们已经发现，COMP可以与聚集素结合，也可以与软骨细胞和成纤维细胞中的整合素结合。此外，在TSP-1-、TSP-3-和CoMP缺失的小鼠中也观察到生长板的解体。我们最近用X射线结晶学解决了CoMP的特征结构域的结构。基于这些数据，我们计划在完整分子和重组签名结构域的背景下，通过定点突变来确定COMP与胶原蛋白、整合素和糖胺多聚糖(GAG)相互作用的分子基础。组成潜在的金属离子依赖的黏附位点(MIDAS)和邻近MIDAS基序的天冬氨酸将被突变为丙氨酸，以确定这些位点在胶原和锌结合以及基质组装中的重要性。此外，还将利用多肽文库探索MIDAS的特异性。GAG的结合部位将通过X射线结晶学进行鉴定。现有的结构数据、自然发生的突变和已发表的合成肽数据将被用来识别用于突变的氨基酸。这种方法将使我们能够在正确折叠的蛋白质的背景下探索特定基序的功能。具体目的2.确定COMP对细胞表型和细胞外基质结构的影响。COMP在生长板发育过程中协调胶原纤维的形成、细胞外基质的组织以及软骨细胞的存活和分化。COMP的重要性被其自然发生的突变导致骨骼发育不良的事实所强调。在目标1中，我们将确定COMP分子中的整合素、胶原和GAG结合部位。在这个目标中，我们将在软骨细胞和成纤维细胞中鉴定整合素介导的细胞对COMP的反应。我们还将利用COMP缺失小鼠的软骨细胞原代培养来探索COMP表达缺失的影响。我们假设野生型comp在抑制细胞凋亡的同时促进细胞的黏附、迁移、增殖和存活。在2-D和3-D培养系统中，介导细胞对COMP反应的特定信号通路将被识别。此外，还将分析野生型和comp缺失型小鼠生长板的增殖、凋亡和基质结构。我们还将确定整合素和GAG结合位点是否与胶原结合位点协作调节ECM结构。最后，我们将探讨一些致病突变对COMP支持细胞过程和基质组装能力的影响。这些研究的数据将为CoMP的签名结构域与各种蛋白质、PG和细胞相互作用的功能提供关键的见解。

A detailed comprehension of the role of the thrombospondins (TSPs), including cartilage oligomeric matrix protein (COMP), in the regulation of extracellular matrix (ECM) structure and cellular behavior during tissue genesis and repair is the long-term goal of the proposed studies. Specific focus for the next period of support will be on the following areas. Specific Aim 1. To identify key amino acids for the interactions of COMP with proteins and proteoglycans (PGs). We have found that COMP binds to aggrecan, as well as to integrins in chondrocytes and fibroblasts. In addition, growth plate disorganization is observed in TSP-1-, TSP-3-, and COMP-null mice. We have recently solved the structure of the signature domain of COMP by X-ray crystallography. Based on these data, we plan to determine the molecular basis for the interaction of COMP with collagens, integrins, and glycosaminoglycans (GAGs) by site-directed mutagenesis within the context of the intact molecule and the recombinant signature domain. The aspartic acids that comprise the potential metal ion-dependent adhesion site (MIDAS) and the adjacent to MIDAS motif will be mutated to alanines to establish the importance of these sites in collagen and zinc binding, and matrix assembly. In addition, the specificity of the MIDAS will be explored using peptide libraries. The binding site for GAGs will be identified by X-ray crystallography. Existing structural data, naturally occurring mutations, and published synthetic peptide data will be used to identify amino acids for mutagenesis. This approach will enable us to probe the function of specific motifs within the context of the correctly folded protein. Specific Aim 2. To determine the effects of COMP on cellular phenotype and ECM structure. COMP orchestrates collagen fibril formation, ECM organization, and chondrocyte survival and differentiation during growth plate development. The importance of COMP is underscored by the fact that naturally occurring mutations in it result in skeletal dysplasias. In Aim 1, we will identify the integrin, collagen and GAG binding sites in the COMP molecule. In this aim, we will identify the integrin-mediated cellular responses to COMP in chondrocytes and fibroblasts. We will also explore the effect of the absence of COMP expression using primary cultures of chondrocytes from COMP-null mice. We hypothesize that wild-type COMP promotes cell adhesion, migration, proliferation and survival, while suppressing apoptosis. The specific signaling pathways that mediate the cellular responses to COMP in 2- and 3-D culture systems will be identified. In addition, proliferation, apoptosis and matrix structure in the growth plate of wild-type and COMP-null mice will be analyzed. We will also determine whether or not the integrin and GAG binding sites collaborate with the collagen-binding site to regulate ECM structure. Finally, we will explore the effect of some of the disease causing mutations on the ability of COMP to support cellular processes and matrix assembly. The data from these studies will provide key insights into the function of the signature domain of COMP in terms of its interactions with various proteins, PGs and cells.