Mannostatin A, a new glycoprotein-processing inhibitor.
Mannostatin A, a new glycoprotein-processing inhibitor.
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Mannostatin A，一种新型糖蛋白加工抑制剂。
DOI：
10.1021/bi00495a008
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发表时间：
1990
期刊：
影响因子：
2.9
通讯作者：
Elbein,AD
中科院分区：
文献类型：
--
作者：
Tropea,JE;Kaushal,GP;Pastuszak,I;Mitchell,M;Aoyagi,T;Molyneux,RJ;Elbein,AD
甘露醇抑制素A是由轮枝链霉菌产生的代谢产物，据报道是大鼠附睾甘露糖苷酶的有效竞争性抑制剂。当针对许多其他芳基糖苷酶进行测试时，甘露聚糖抑制素A对α-和β-葡糖苷酶和半乳糖苷酶以及β-甘露糖苷酶无活性，但它是刀豆、绿豆和大鼠肝溶酶体-甘露糖苷酶的有效抑制剂，估计的IC 50分别为70 nM、450 nM和160 nM。抑制的类型是竞争性的。该化合物也被证明是糖蛋白加工酶甘露糖苷酶II的有效竞争性抑制剂（以对硝基苯基α D-甘露-吡喃糖苷为底物的IC 50约为10-15 nM，以[3 H]甘露糖标记的GlcNAc-Man 5GlcNAc为底物的IC 50约为90 nM）。然而，它实际上对甘露糖苷酶I无活性。甘露糖抑制素A的N-乙酰化衍生物没有抑制活性。在细胞培养研究中，甘露醇抑制素A也被证明是糖蛋白加工的有效抑制剂。因此，在流感病毒感染的Madin达比犬肾（MDCK）细胞中，甘露聚糖酶抑制剂A阻断了病毒糖蛋白上复合型寡糖的正常形成，并引起杂合型寡糖的积累。这一观察结果与其他数据一致，这些数据表明甘露糖抑制素A的作用位点是甘露糖苷酶II。因此，mannostatin A代表了第一个非类固醇加工抑制剂，并增加了越来越多的化学结构，可以有重要的生物活性。糖蛋白是一组种类繁多的生物聚合物，是几乎所有生命形式的普遍存在的组成部分。它们以可溶性和膜结合形式存在于细胞中，以及存在于细胞内基质和细胞外液中。这类化合物包括酶、免疫球蛋白、激素、转运蛋白、毒素、凝集素和结构蛋白等（Wagh & Bahl，1981）。多年来，已经变得明显的是，糖蛋白的碳水化合物部分不执行单一功能，而是以多种方式起作用，这可能取决于它们出现的糖蛋白（奥登et al.，1982年）。在一些情况下，糖侧链可直接参与糖蛋白的生物活性（Dahms等人，1989），而在其他情况下，它可以执行许多不太明显的辅助功能中的任何一种（Rademacher等人，1988年）。在自然界中发现的常见类型的糖蛋白是具有N-连接的或天冬酰胺连接的寡糖的糖蛋白（Kornfeld & Kornfeld，1985）。这些N-连接糖蛋白的寡糖部分的生物合成涉及一系列复杂的事件，可分为三个一般步骤：（1）合成共同中间体Glc 3 Mang（GlcNAc）2-焦磷酸-多萜醇，（2）将该共同前体的寡糖部分转移至蛋白质上的特定天冬酰胺残基，（3）修剪碳水化合物单元并添加外围糖和其他成分，以产生各种不同的寡糖侧链（Hubbard & Ivatt，1981）。步骤1和2出现
Mannostatin A is a metabolite produced by the microorganism Streptoverticillium verticillus and reported to be a potent competitive inhibitor of rat epididymal-mannosidase. When tested against a number of other arylglycosidases, mannostatin A was inactive toward a-and/3-glucosidase and galactosidase as well as^-mannosidase, but it was a potent inhibitor of jack bean, mung bean, and rat liver lysosomal-mannosidases, with estimated IC50’s of 70 nM, 450 nM, and 160 nM, respectively. The type of inhibition was competitive in nature. This compound also proved to be an effective competitive inhibitor of the glycoprotein-processing enzyme mannosidase II (IC50 of about 10-15 nM with p-nitrophenyl aD-manno-pyranoside as substrate, and about 90 nM with [3H] mannose-labeled GlcNAc-Man5GlcNAc as substrate). However, it was virtually inactive toward mannosidase I. The N-acetylated derivative of mannostatin A had no inhibitory activity. In cell culture studies, mannostatin A also proved to be a potent inhibitor of glycoprotein processing. Thus, in influenza virus infected Madin Darby canine kidney (MDCK) cells, mannostatin A blocked the normal formationof complex types of oligosaccharides on the viral glycoproteins and caused the accumulation of hybrid types of oligosaccharides. This observation is in keeping with other data which indicate that the site of action of mannostatin A is mannosidase II. Thus, mannostatin A represents the first nonalkaloidal processing inhibitor and adds to the growing listof chemical structures that can have important biological activity.(jlycoproteins are a most diverse group of biologicalpoly-mers that are ubiquitous constituents of nearly all forms of life. They occur in cells, in both soluble and membrane-bound form, as well as in the intracellular matrix and extracellular fluids. Included in this class of compounds are enzymes, immunoglobulins, hormones, transport proteins, toxins, lectins, and structural proteins, to name a few (Wagh & Bahl, 1981). Over the years, it has becomeapparent that the carbohydrate portions of glycoproteins do not perform a single function but act in a variety of ways, probably depending on the glycoprotein in which they occur(Olden et al., 1982). In some cases, the sugar side chain may be directly involved in the biological activity of the glycoprotein (Dahms et al., 1989), whereas in other cases, it may perform any of a number of less obvious ancillary functions (Rademacher et al., 1988). Among the common types of glycoproteins that are found in nature are those having N-linked or asparagine-linked oligosaccharides (Kornfeld & Kornfeld, 1985). The biosynthesis of the oligosaccharide portion of these N-linked glycoproteins involves a complex sequence of events that can be divided into three general steps:(1) synthesis of the common intermediate, Glc3Mang (GlcNAc) 2-pyrophosphoryl-dolichol,(2) transfer of the oligosaccharide portion of this common precursor to spe-cific asparagine residues on the protein, and (3) trimming of the carbohydrate unit and addition of peripheral sugars and other constituents to give a variety of different oligosaccharide side chains (Hubbard & Ivatt, 1981). Steps 1 and 2 appear