酵素唾液酸化 Globo-系列醣體

Enzymatic Sialylation of Globo-Series Glycans

郭力禎(Li-Jhen Guo)

指導教授 ： 林俊成

國立清華大學/理學院/化學系/碩士(2015年)

摘要

研究指出 DSGb5 和 SSEA4 為腫瘤相關抗原，Globo 系列的唾液酸化醣苷神經鞘脂可能為參與生理活動的重要抗原標記。除此之外，自然界中唾液酸通常被修飾於醣體末端。唾液酸化醣體在多樣化的生理活動中扮演關鍵的角色。唾液酸免疫球蛋白凝集素對不同的含唾液酸基配體，擁有不同的專一性辨識位。特定的鎖鑰辨識可刺激或抑制免疫訊號。近年研究顯示唾液酸免疫球蛋白凝集素或許能視為治療對象。此外，合成的醣配體已被證實為一有價值的工具，能用來解釋唾液酸免疫球蛋白凝集素與配體間的交互作用與疾病的關係。
由於酵素合成的高度立體位向選擇性，以酵素為催化劑的研究，於醣體合成領域快速發展成具前景性的方法。本論文中，使用來自嗜血流感桿菌的醣基轉移酶 LgtD，以及大腸桿菌的尿苷轉移酶 GlmU 做為建構 globo 醣體的關鍵酵素。為了合成複雜唾液酸基化碳水化合物，我們組合 LgtD、GlmU 以及其他8種酵素，包括醣激酶、尿苷轉移酶、醣基轉移酶、唾液酸轉移酶。藉由使用不同來源的唾液酸轉移酶，成功建立唾液酸基化 globo 醣體分子庫，其中包含：α-2,3-sialyl-Gb3, α-2,6-sialyl-Gb3, α-2,3-sialyl-Gb4 以及 α-2,6-sialyl-Gb4。這些分子可作為起始物，供進一步碳水化合物生物活性之研究。

關鍵字

酵素 ； 醣 ； 唾液酸

並列摘要

Studies indicate DSGb5 and SSEA4 are tumor associated antigens. Globo-series ganglioside may be important epitopes involving in biological events. In addition, sialic acids are usually decorated at the terminal position of glycan chain in nature. It is not surprising that sialosides play critical roles in diverse biological process. Sialic acid-binding Ig-like lectins (Siglecs) possess different specific recognition sites to different sialic acid containing ligands. Specific lock-and-key recognition can stimulate or inhibit immunnal signals. Recent studies have showned Siglecs may serve as therapic candidates. Furthermore, it is proven that synthetic glycan ligands are valuable tools for elucidating relationship between siglec-ligand interaction and disease.
Due to the high regio- and stereo-selectivity of enzymatic synthesis, researches of enzymes as catalysts have grown rapidily and becomed promising methods in oligosaccharide synthesis. In this thesis, glycosyltransferase (LgtD from Haemophilus influenzae) and uridyltransferase (GlmU from E. coli) were chosen as key enzymes and used to construct globoside. We assembled LgtD, GlmU and the other 8 kinds of enzymes, including kinase, uridyltransferase, glycosyltransferase, and sialyltransferase for complicated sialylated carbohydrate synthesis. A globo-sialoside library, α-2,3-sialyl-Gb3, α-2,6-sialyl-Gb3, α-2,3-sialyl-Gb4 and α-2,6-sialyl-Gb4, was successfully establish by using different source of sialyltransferases. These molecules can serve as starting materials for further carbohydrate bioactivity researches.

並列關鍵字

globo ； enzyme ； sugar ； sialic acid

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