Heese-Peck A, Cole R N, Borkhsenious O N, Hart G W, Raikhel N V
Michigan State University, Department of Energy Plant Research Laboratory, East Lansing 48824-1312, USA.
Plant Cell. 1995 Sep;7(9):1459-71. doi: 10.1105/tpc.7.9.1459.
Only a few nuclear pore complex (NPC) proteins, mainly in vertebrates and yeast but none in plants, have been well characterized. As an initial step to identify plant NPC proteins, we examined whether NPC proteins from tobacco are modified by N-acetylglucosamine (GlcNAc). Using wheat germ agglutinin, a lectin that binds specifically to GlcNAc in plants, specific labeling was often found associated with or adjacent to NPCs. Nuclear proteins containing GlcNAc can be partially extracted by 0.5 M salt, as shown by a wheat germ agglutinin blot assay, and at least eight extracted proteins were modified by terminal GlcNAc, as determined by in vitro galactosyltransferase assays. Sugar analysis indicated that the plant glycans with terminal GlcNAc differ from the single O-linked GlcNAc of vertebrate NPC proteins in that they consist of oligosaccharides that are larger in size than five GlcNAc residues. Most of these appear to be bound to proteins via a hydroxyl group. This novel oligosaccharide modification may convey properties to the plant NPC that are different from those of vertebrate NPCs.
只有少数几种核孔复合体（NPC）蛋白得到了充分表征，主要存在于脊椎动物和酵母中，而植物中则没有。作为鉴定植物NPC蛋白的第一步，我们检测了烟草中的NPC蛋白是否被N-乙酰葡糖胺（GlcNAc）修饰。使用小麦胚凝集素（一种能特异性结合植物中GlcNAc的凝集素），经常发现特异性标记与NPC相关或相邻。通过小麦胚凝集素印迹分析表明，含有GlcNAc的核蛋白可以用0.5M盐部分提取，并且通过体外半乳糖基转移酶分析确定，至少有八种提取的蛋白被末端GlcNAc修饰。糖分析表明，具有末端GlcNAc的植物聚糖不同于脊椎动物NPC蛋白的单个O-连接GlcNAc，因为它们由大小超过五个GlcNAc残基的寡糖组成。其中大多数似乎通过羟基与蛋白质结合。这种新的寡糖修饰可能赋予植物NPC与脊椎动物NPC不同的特性。
