STRUCTURE AND FUNCTION OF SURFACTANT PROTEIN D

表面活性蛋白D(SP-D)是一种胶原性碳水化合物结合蛋白 由肺泡型II型分泌到肺的空气中 无纤毛的细支气管上皮细胞。SP-D分子由四个分子组成 三聚体亚基，每个具有约100 nm的三螺旋臂和一个 碳水化合物结合域的羧基末端簇(CRD)。这个 三聚体亚基的氨基末端是交联的，而SP-D 分子可以进一步与外周缔合形成星状多聚体 多达32个三聚体CRD阵列。SP-D显示凝集素依赖 在体外与白细胞和各种微生物相互作用， 提示它在肺反应中起重要作用 微生物挑战。此外，多价性和 参与与空间分离的糖共轭化合物的相互作用 似乎对SP-D功能很重要。出于这些原因，它是 重要的是要了解分子和细胞机制 调节SP-D及其后续的复杂分子组装 在空域中积聚。在本申请中，我们提出了两个 明确的目标。首先，我们将利用生化、分子和细胞 培养技术以阐明细胞内所需的事件 SP-D分子和多聚体的生产。对于这些研究，我们将使用 转基因哺乳动物细胞(CHO-K1)模型系统的建立 野生型或突变型SP-D，以研究分泌途径和 分子组装的结构要求。第二，我们将 研究人类SP-D基因的转录调控， 关注糖皮质激素对SP-D基因表达的调节 组织限制性表达的控制。这些研究将提供 与SP-D生产和监管有关的重要新信息 增加我们对潜在细胞调控机制的理解 非免疫性肺宿主防御。这种机制在以下方面很重要 身体最初与吸入病原体的接触，并可能假设 在不成熟或免疫功能受损的环境中起关键作用。

Surfactant Protein D (SP-D) is a collagenous carbohydrate binding protein that is secreted into the airspaces of the lung by alveolar type II and nonciliated bronchiolar epithelial cells. SP-D molecules consist of four trimeric subunits, each with about 100 nm triple-helical arm and a carboxy-terminal cluster of carbohydrate binding domains (CRD). The trimeric subunits are crosslinked at their amino-termini, and SP-D molecules can further associate to form stellate multimers with peripheral arrays of up to 32 trimeric CRDs. SP-D shows lectin-dependent interactions with leukocytes and a variety of microorganisms in vitro, suggesting that it plays important roles in the pulmonary response to microbial challenge. Furthermore, multivalency and the capacity to participate in interactions with spatially separated glycoconjugates appears to be important for SP-D function. For these reasons, it is important to understand the molecular and cellular mechanisms that regulate the complex molecular assembly of SP-D and its subsequent accumulation in the airspace. In this application, we propose two specific aims. First, we will employ biochemical, molecular, and cell culture techniques to elucidate the intracellular events required for the production of SP-D molecules and multimers. For these studies we will use a model system consisting of mammalian cells (CHO-K1) transfected with wild-type or mutant SP-Ds in order to study the pathway of secretion and the structural requirements for molecular assembly. Second, we will investigate the transcriptional regulation of the human SP-D gene, focusing on the modulation of SP-D gene expression by glucocorticoids and the control of tissue-restricted expression. These studies will provide important new information related to the regulation of SP-D production and increase our understanding of potential cellular mechanisms regulating non-immune pulmonary host defense. Such mechanisms are important during the body's initial encounter with inhaled pathogens, and may assume a critical role in the settings of immature or impaired immune function.