Cellular protein maturation and degradation

本提案的总体目标是确定N-连接聚糖在 通过分泌途径的蛋白质的成熟和质量控制。的 大多数通过分泌途径的蛋白质接受多个N-连接的 糖基化我们和其他人已经表明，这些碳水化合物被用作 成熟和质量控制信号，以传达关于 使新生的链条成熟，并帮助决定它们的命运。信息 蛋白质的构象在N-连接聚糖的组成内由蛋白质构象编码。 位于内质网（ER）中的一系列糖苷酶和转移酶。 这些编码蛋白能够基于糖基化调节聚糖组成。 蛋白质的结构。UDP-葡萄糖：糖蛋白葡糖基转移酶（GT 1）是 目前唯一已知的可以改变聚糖结构的蛋白质， 修饰蛋白质的性质，但很少有人知道它在活细胞中的活性。的 然后，聚糖组成被碳水化合物结合蛋白破译， 不同的聚糖结构，并作为分子伴侣或分选受体，以帮助 在成熟和质量控制过程中。碳水化合物的葡萄糖臂 支持凝集素伴侣钙连接蛋白和钙网蛋白的结合，钙连接蛋白和钙网蛋白指导其共 和翻译后折叠过程。相比之下，甘露糖分支似乎 在引导蛋白质离开内质网中起重要作用。天然蛋白质是 发送到高尔基体，而异常蛋白质被细胞溶质破坏 蛋白酶体通过ER相关蛋白降解（ERAD）途径。因此，我们认为， 甘露聚糖酶似乎参与产生质量控制代码， 被碳水化合物结合分选受体识别， ER的蛋白质。这种由酶组成的内质网可以修饰和识别聚糖 基于修饰蛋白质的构象， 成熟过程和指导质量控制运输的糖蛋白在分泌 通路我们的具体目标：（1）了解聚糖的作用和载体性质 在鞘脂激活蛋白原的有效成熟中，细胞折叠反应的顺序 （2）阐明GT 1在细胞成熟过程中的功能， 鞘脂激活蛋白原（一种专性GT 1底物）的质量控制;以及（3）确定 甘露聚糖酶样蛋白，EDEM 1，在非天然蛋白的分选和递送中 ER相关蛋白降解途径。

The overall goal of this proposal is to determine the role of N-linked glycans in the maturation and quality control of proteins that traverse the secretory pathway. The majority of proteins that travel through the secretory pathway receive multiple N-linked glycosylations. We and others have shown that these carbohydrates are used as maturation and quality control signals to convey information about the fitness of maturing nascent chains and help to determine their fate. Information about the conformation of a protein is encoded within the composition of the N-linked glycan by a series of glycosidases and transferases that reside in the endoplasmic reticulum (ER). These encoder proteins are able to modulate the glycan composition based on the structure of the protein. The UDP-glucose: glycoprotein glucosyltransferase (GT1) is currently the only known protein that can modify the glycan structure dependent upon the properties of the modified protein, yet little is known about its activity in live cells. The glycan composition is then deciphered by carbohydrate-binding proteins that recognize distinct glycan structures and act as molecular chaperones or sorting receptors to assist in maturation and quality control processes. The glucose arm of the carbohydrate supports binding by the lectin chaperones calnexin and calreticulin, which direct its co- and post-translational folding processes. In contrast, the mannose branches appear to serve important roles for directing the exit of proteins from the ER. Native proteins are sent to the Golgi, whereas aberrant proteins are sorted for destruction by the cytosolic proteasome through the ER-associated protein degradation (ERAD) pathway. Therefore, mannosidases appear to be involved in generating the quality control code that is recognized by carbohydrate-binding sorting receptors that control the trafficking of proteins from the ER. This ER network of enzymes that modify and recognize glycans based on the conformation of the modified protein plays a crucial role in assisting the maturation process and directing quality control traffic of glycoproteins in the secretory pathway. Our specific aims: (1) to understand the role of glycans and the vectorial nature of the cellular folding reaction in the efficient maturation of prosaposin, a sequential domain containing protein; (2) to elucidate the function of GT1 in the maturation and quality control of prosaposin, an obligate GT1 substrate; and (3) to determine the role of the mannosidase-like protein, EDEM1, in the sorting and delivery of non-native proteins to the ER-associated protein degradation pathway.