Chemoenzymatic glycan editing for deciphering biological functions of glycans

项目概要/摘要 细胞表面聚糖参与许多生物学过程，包括信号转导、细胞-细胞 沟通与发展。异常糖基化是人类疾病的标志。在分子水平上， 聚糖代表细胞之间的第一接触点。然而，这些基因不是直接编码在基因组中， 单独使用分子生物学技术来研究生物分子具有挑战性。代谢寡糖 在20世纪90年代后期发展起来的MOE（MoE）已经彻底改变了标记和可视化的方式， 生物体内的聚糖。在这种方法中，细胞自身的聚糖生物合成机制被劫持， 具有键混杂性的非天然单糖。 作为莫伊的补充，化学酶聚糖编辑已经成为探测和分析聚糖的有价值的工具。 修饰细胞环境中的聚糖结构。与莫伊不同，化学酶聚糖修饰 利用重组糖基转移酶转移具有新功能的天然或非天然单糖 从活化的核苷酸糖到细胞表面上具有连接特异性的糖缀合物。为这些 因此，化学酶聚糖修饰提供了一种简便和更精确的方法来探测功能， 在它们的自然环境中。 在我们成功应用化学酶聚糖编辑的基础上，在未来五年内，我们将 扩展我们的化学酶工具包，以研究聚糖的细胞功能，重点是N- 乙酰乳糖胺（LacNAc）、岩藻糖和唾液酸在免疫调节中的作用。细胞表面LacNAc介导 配体-受体结合，并设定用于启动免疫细胞活化的下游信号传导的阈值。 LacNAc残基被唾液酸和/或岩藻糖动态修饰。然而，这些具体的作用 免疫调节和疾病进展的改变仍然不清楚。 我们特别感兴趣的是发现：（1）LacNAc和岩藻糖基化状态的变化是否可以 作为T细胞耗竭的聚糖标志，在此期间T细胞逐渐失去其细胞因子产生， （2）细胞表面原位LacNAc岩藻糖基化是否可用于增强细胞增殖和细胞毒能力？ T细胞和NK细胞的抗肿瘤免疫效力？同时，我们将开发化学酶工具， 分析Siglecs的唾液酸化糖蛋白配体（唾液酸结合免疫球蛋白型凝集素）和Siglecs的唾液酸化糖蛋白配体（唾液酸结合免疫球蛋白型凝集素）， 鉴定非天然、高亲和力和特异性配体以询问Siglec功能。 通过这些研究，我们将更深入地了解LacNAc、岩藻糖和唾液酸是如何与 参与调节免疫细胞活化、效应子功能和耗竭。开发工具 该项目也可用于研究其他类型的聚糖及其与聚糖结合蛋白的相互作用。

PROJECT SUMMARY/ABSTRACT Cell-surface glycans participate in numerous biological processes, including signal transduction, cell-cell communication and development. Aberrant glycosylation is a hallmark of human disease. At a molecular level, glycans represent the first points of contact between cells. However, not directly encoded in the genome, these biomolecules are challenging to study using molecular biology techniques alone. Metabolic oligosaccharide engineering (MOE) developed in late 1990’s has revolutionized the way for the labeling and visualization of glycans in living organisms. In this method, cells’ own glycan biosynthetic machinery is hijacked to incorporate unnatural monosaccharides with linkage promiscuity. Complementary to MOE, chemoenzymatic glycan editing has emerged as a valuable tool to probe and modify glycan structures within a cellular environment. Unlike MOE, chemoenzymatic glycan modification utilizes recombinant glycosyltransferases to transfer natural or unnatural monosaccharides with novel functions from activated nucleotide sugars to glycoconjugates on the cell surface with linkage specificity. For these reasons, chemoenzymatic glycan modification provides a facile and more precise way for probing the function of glycans in their native environments. Building upon our successful application of chemoenzymatic glycan editing, in the next five years we will expand our chemoenzymatic tool kits to study glycans’ cellular functions with a focus on the special roles of N- acetyllactosamine (LacNAc), fucose and sialic acid in immune regulation. Cell-surface LacNAc mediates ligand-receptor binding and sets a threshold for initiating the downstream signaling for immune cell activation. LacNAc residues are dynamically modified by sialic acid and/or fucose. However, the specific roles of these modifications in immune regulation and disease progression remain obscure. We are particularly interested in finding out: (1) if changes in LacNAc and fucosylation status can serve as glycan signatures of T cell exhaustion during which T cells gradually lose their cytokine production, proliferation and cytotoxic capacity; (2) Can cell-surface in situ LacNAc fucosylation be used to boost the efficacy of antitumor immunity of T cells and NK cells? In parallel, we will develop chemoenzymatic tools for profiling sialylated glycoprotein ligands of Siglecs (sialic acid-binding immunoglobulin-type lectins) and for the identification of unnatural, high-affinity and specific ligands to interrogate Siglec functions. Through these studies, we will gain a deeper understanding of how LacNAc, fucose and sialic acid are involved in the regulation of the immune cell activation, effector function and exhaustion. Tools developed in this project can also be used to study other types of glycans and their interactions with glycan binding proteins.