Crowell DN, Sen SE, Randall SK
Department of Biology, Indiana University-Purdue University at Indianapolis, 723 West Michigan Street, Indianapolis, Indiana 46202 (D.N.C., S.K.R.).
Plant Physiol. 1998 Sep;118(1):115-23. doi: 10.1104/pp.118.1.115.
Isoprenylation is a posttranslational modification that is believed to be necessary, but not sufficient, for the efficient association of numerous eukaryotic cell proteins with membranes. Additional modifications have been shown to be required for proper intracellular targeting and function of certain isoprenylated proteins in mammalian and yeast cells. Although protein isoprenylation has been demonstrated in plants, postisoprenylation processing of plant proteins has not been described. Here we demonstrate that cultured tobacco (Nicotiana tabacum cv Bright Yellow-2) cells contain farnesylcysteine and geranylgeranylcysteine alpha-carboxyl methyltransferase activities with apparent Michaelis constants of 73 and 21 &mgr;M for N-acetyl-S-trans, trans-farnesyl-L-cysteine and N-acetyl-S-all-trans-geranylgeranyl-L-cysteine, respectively. Furthermore, competition analysis indicates that the same enzyme is responsible for both activities. These results suggest that alpha-carboxyl methylation is a step in the maturation of isoprenylated proteins in plants.
异戊二烯化是一种翻译后修饰，被认为是众多真核细胞蛋白与膜高效结合所必需的，但并非充分条件。在哺乳动物和酵母细胞中，已证明某些异戊二烯化蛋白的正确细胞内靶向和功能还需要额外的修饰。虽然植物中已证实存在蛋白质异戊二烯化，但尚未描述植物蛋白的异戊二烯化后加工过程。在此，我们证明培养的烟草（Nicotiana tabacum cv Bright Yellow-2）细胞含有法尼基半胱氨酸和香叶基香叶基半胱氨酸α-羧基甲基转移酶活性，对N-乙酰-S-反式，反式-法尼基-L-半胱氨酸和N-乙酰-S-全反式-香叶基香叶基-L-半胱氨酸的表观米氏常数分别为73和21μM。此外，竞争分析表明这两种活性由同一种酶负责。这些结果表明α-羧基甲基化是植物中异戊二烯化蛋白成熟过程中的一个步骤。
