AbstractSialic acids, terminal sugars of glycoproteins and glycolipids, play important roles in development, cellular recognition processes and host–pathogen interactions. A common modification of sialic acids is 9-O-acetylation, which has been implicated in sialoglycan recognition, ganglioside biology, and the survival and drug resistance of acute lymphoblastic leukaemia cells. Despite many functional implications, the molecular basis of 9-O-acetylation has remained elusive thus far. Following cellular approaches, including selective gene knockout by CRISPR/Cas genome editing, we here show that CASD1—a previously identified human candidate gene—is essential for sialic acid 9-O-acetylation. In vitro assays with the purified N-terminal luminal domain of CASD1 demonstrate transfer of acetyl groups from acetyl-coenzyme A to CMP-activated sialic acid and formation of a covalent acetyl-enzyme intermediate. Our study provides direct evidence that CASD1 is a sialate O-acetyltransferase and serves as key enzyme in the biosynthesis of 9-O-acetylated sialoglycans.
摘要唾液酸是糖蛋白和糖脂的末端糖,对于发育、细胞识别过程和宿主-病原体相互作用起着重要作用。唾液酸的常见修饰是9-O-乙酰化,已被证明在唾液糖基的识别、神经节苷脂生物学以及急性淋巴细胞白血病细胞的存活和抗药性中起着重要作用。尽管有许多功能意义,但9-O-乙酰化的分子基础迄今仍然不清楚。通过细胞方法,包括CRISPR/Cas基因组编辑的选择性基因敲除,我们在这里展示了之前鉴定的人类候选基因CASD1对唾液酸9-O-乙酰化是必不可少的。通过对CASD1纯化的N端腔内结构域的in vitro测定,我们证明了乙酰辅酶A向CMP激活的唾液酸转移乙酰基的形成,以及形成共价的乙酰-酶中间体。我们的研究提供了直接证据,证明CASD1是一种唾液酸O-乙酰转移酶,是合成9-O-乙酰化唾液糖基的关键酶。