Sialyl hydrolases, trans-sialidases, and sialyl transferases are biologically important enzymes that are responsible for the incorporation and removal of sialic acid residues, which decorate many cell surface glycocongugates. Two fluorinated sialic acid derivatives have been synthesized as mechanism-based inactivators, to probe the catalytic mechanisms through which sialidases and trans-sialidases operate. Both compounds are known to be covalent inactivators of a trans-sialidase from Trypanosoma cruzi. Here, 3-fluorosialosyl fluoride has been found to covalently label the catalytic nucleophile of a sialidase from T. rangeli, and the residue involved is shown to be Tyr346 within the sequence DENSGYSSVL. This is the first demonstration that sialidases operate through a covalent glycosyl-enzyme intermediate, strongly suggesting a common catalytic mechanism amongst all members of the sialidase superfamily. CMP-3-fluoro sialic acid is a competitive inhibitor of sialyl transferases and was synthesized via a two-step enzymatic process from commercially available N-acetyl mannosamine, 3-fluoropyruvic acid, and cytidine triphosphate in around 84% yield.Key words: sialidase, mechanism, labeling, nucleophile, inhibitor.
唾液酸水解酶、转唾液酶和唾液酸转移酶是生物学上重要的酶,负责将唾液酸残基纳入或去除许多细胞表面糖蛋白中。已合成两种氟代唾液酸衍生物作为机理基础失活剂,以探究唾液酸水解酶和转唾液酶的催化机制。这两种化合物已知是Trypanosoma cruzi的一种转唾液酶的共价失活剂。在这里,发现3-氟唾液酸氟化物能共价标记T. rangeli的一种唾液酸水解酶的催化亲核物,涉及的残基为DENSGYSSVL序列中的Tyr346。这是首次证明唾液酸水解酶通过共价糖基-酶中间体进行催化,强烈暗示唾液酸水解酶超家族的所有成员之间存在共同的催化机制。CMP-3-氟唾液酸是一种唾液酸转移酶的竞争性抑制剂,通过从商业可得的N-乙酰甘露胺、3-氟丙酮酸和胞嘧啶三磷酸的两步酶法过程中合成,产率约为84%。关键词:唾液酸水解酶、机制、标记、亲核物、抑制剂。