REGULATION OF MUCIN GLYCOPROTEIN BIOSYNTHESIS

O-糖基化是粘蛋白的重要功能决定因素， 赋予粘液外壳独特保护作用的糖蛋白 品质。然而，在我们对这一问题的理解中仍然存在一个严重的差距 调节O-糖基化启动的事件。小才是 已知粘蛋白核心蛋白(无粘蛋白)是如何表达的 是受控制的。我们假设apomucin的表达是 以特定于组织的方式调节，并且这种差异 不同蛋白质核心的糖基化是造成异质性的原因 在粘蛋白结构中观察到。为了检验这一假设，我们建议 鉴定和鉴定编码rSMG无蛋白粘蛋白的cDNA。这些cDNA 将用于推导无粘蛋白的氨基酸序列(S)和 将被用作探针来确定组织和细胞 编码粘蛋白核心蛋白的转录本的分布。 也不清楚为什么一些蛋白质会变成O-糖基化，而 其他的则不会被修改。我们假设O-的位置- 蛋白质中的糖基化是由分子信号引导的，分子信号 都包含在编码 糖蛋白的蛋白质核心。为了检验这一假设，我们建议 表达血糖蛋白A(一种特性良好的O-糖基化蛋白)，或 富含谷氨酰胺/谷氨酸的蛋白质(一种缺乏 异种细胞系(中国仓鼠卵巢细胞)中的糖) 并确定每个重组体中的哪些潜在受体位点 分子被糖基化。特定序列和构象 血糖素A和谷氨酰胺/谷氨酸富含蛋白的结构域 检测其促进或抑制O-糖基化的能力。 这些研究将使我们能够确定信号的性质 直接进行O-糖基化。这些信息将极大地促进 重组人设计生物活性O-糖基化蛋白的尝试 DNA方法。此外，更透彻地了解正常 O-糖基化的过程可能提供对特定形式的 被认为与粘蛋白的异常有关的病理学- 糖蛋白生物合成。

O-glycosylation represents a crucial functional determinant of mucins, the glycoproteins which endow the mucus coat with its unique protective qualities. However, a critical gap remains in our understanding of the events which regulate the initiation of O-glycosylation. Little is known about how the expression of the protein core of mucin (apomucin) is controlled. We hypothesized that the expression of apomucin is regulated in a tissue-specific manner and that differential glycosylation of variant protein cores contributes to the heterogeneity observed in mucin structure. To test this hypothesis we propose to identify and characterize cDNAs which encode RSMG apomucin. These cDNAs will be used to deduce the amino acid sequence of the apomucin(s) and will be used as a probe to determine the tissue and cellular distribution of transcripts which encode the protein core of the mucin. It is also unclear why some proteins become O-glycosylated whereas others do not become modified. We hypothesize that the sites of O- glycosylation within a protein are directed by molecular signals which are embodied within the information contained in the mRNA encoding the protein core of the glycoprotein. To test this hypothesis we propose to express glycophorin A (a well-characterized O-glycosylated protein), or glutamine/glutamic acid-rich protein (a protein which is devoid of saccharide) in a heterologous cell line (Chinese Hamster Ovary cells) and determine which potential acceptor sites in each recombinant molecule become glycosylated. Specific sequence and conformational domains of glycophorin A and glutamine/glutamic acid-rich protein will be assayed for their ability to promote or inhibit O-glycosylation. These studies will enable us to determine the nature of the signals which direct O-glycosylation. This information would greatly facilitate attempts to engineer bioactive O-glycosylated proteins by recombinant DNA methods. In addition, a more thorough understanding of the normal process of O-glycosylation may provide insight into specific forms of pathology which are thought to be related to aberrations of mucin- glycoprotein biosynthesis.