Chemical strategies to investigate sialic acid processing enzymes

蛋白质的翻译后修饰对这些生物分子的功能是必不可少的，并且通常作为一种关键的生化调节机制。人类细胞中超过一半的蛋白质是糖基化的，这使得糖基化(多糖)成为最丰富的翻译后修饰。在人类中，大多数细胞外和细胞表面的多糖都含有末端唾液酸(也称为神经氨酸)残基。这些唾液酸苷，由于它们位于胞外多糖的外围，通常是细胞-细胞和细胞-病原体相互作用的第一个点。因此，唾液酸苷往往对感染、发育和免疫至关重要。例如，唾液酸苷被病毒用来区分适合感染的宿主细胞，并被我们自己的免疫系统用来识别自我和非我。我们建议扩大我们在唾液酸苷化学生物学方面的研究计划，以开发新的研究工具来了解唾液酸苷及其修饰酶在细胞生物学中的作用。作为我们计划的一部分，我们将确定对肺炎链球菌的细菌神经氨酸酶(neu，也称为唾液酸酶)具有选择性的新的竞争性抑制剂。这些抑制剂将是研究细菌neu在感染中的作用的有价值的新工具。我们计划的一个主要组成部分将是开发新的生物结合物策略，以产生定义的聚唾液酸(PSA)糖结合物和研究它们在细胞中的代谢的工具。这些工具将帮助我们了解PSA糖蛋白的加工过程，并可能为改进治疗性蛋白提供新的工具。我们还将研究参与唾液酸苷生物合成的酶，特别是N-酰基神经氨酸酯-9-磷酸酶(NANP)的特定作用，该酶以前被认为是唾液酸苷生物合成所必需的。基于最近的发现，我们建议开发化学工具来识别体内绕过NANP的替代磷酸酶，以及该酶的特定共价和竞争抑制剂。这些工具将是理解唾液酸在人类细胞中生物合成的基本机制所必需的。这些项目将在唾液酸苷的化学生物学方面形成一个广泛的计划，并将在碳水化合物化学、生物有机化学、药物化学、生物偶联化学、酶学、生物化学和分子生物学方面提供出色的培训。

The post-translational modification of proteins is essential to the function of these biomolecules and often serves as a critical biochemical regulatory mechanism. Over half of all proteins in human cells are glycosylated, making glycosylation (glycans) the most abundant post-translational modification. In humans, most extracellular and cell-surface glycans contain terminal sialic acid (also called neuraminic acid) residues. These sialosides, by virtue of their location at the periphery of extracellular glycans, are often the first point of interaction in cell-cell and cell-pathogen interactions. Thus, sialosides are often critical to infection, development, and immunity. For example, sialosides are used by viruses to distinguish appropriate host cells for infection and by our own immune system to recognize self from non-self. We propose to expand our research program in the chemical biology of sialosides to develop new research tools to understand the role of sialosides, and enzymes that modify them, in cell biology. As part of our program we will identify new competitive inhibitors with selectivity for bacterial neuraminidase enzymes (NEU, also known as sialidases) of S. pneumoniae. These inhibitors will be valuable new tools for studying the role of bacterial NEU in infection. A major component of our program will be the development of new bioconjugate strategies to generate defined polysialic acid (PSA) glycoconjugates and tools to study their metabolism by cells. These tools will help us to understand the processing of PSA glycoproteins and could provide new tools for improving therapeutic proteins. We will also study enzymes involved in the biosynthesis of sialosides in particular, we will examine the specific role of the N-acylneuraminate-9-phosphatase (NANP) that has previously been thought to be essential to sialoside biosynthesis. Based on recent findings, we propose to generate chemical tools to identify alternative phosphatases that bypass NANP in vivo, as well as specific covalent and competitive inhibitors of this enzyme. These tools will be essential to understanding the fundamental mechanisms of sialic acid biosynthesis in human cells. Together these projects will form a broad program in the chemical biology of sialosides and will provide excellent training in carbohydrate chemistry, bioorganic chemistry, medicinal chemistry, bioconjugate chemistry, enzymology, biochemistry, and molecular biology.