Newman C M, Giannakouros T, Hancock J F, Fawell E H, Armstrong J, Magee A I
National Institute for Medical Research, Mill Hill, London, United Kingdom.
J Biol Chem. 1992 Jun 5;267(16):11329-36.
ras proteins are post-translationally processed at their carboxyl-terminal CAAX motif by a triplet of modifications: prenylation of C with farnesyl, proteolytic trimming of AAX, and carboxyl-methylation. These modifications co-operate with palmitoylation of nearby sites or a polybasic region to target plasma membrane localization. The related YPT/rab proteins in contrast are localized to compartments of the endo-membrane system and may be involved in directing membrane traffic. These proteins end in XCC or CXC motifs. We have analyzed the processing of members of this subfamily form the fission yeast Schizosaccharomyces pombe. We find using in vitro translation in reticulocyte lysates that YPT1, -3, and -5 are prenylated with geranylgeranyl and that they incorporate label from [3H]mevalonic acid when expressed in transfected COS cells in vivo. Furthermore, prenylation was necessary for membrane binding in vivo. The CXC protein YPT5, but neither of the two XCC proteins YPT1 and YPT3, was carboxyl-methylated in S. pombe and in COS cells in vivo. However, YPT5 was not carboxyl-methylated in vitro in lysates which were able to methylate ras protein. YPT3 was detectably palmitoylated when expressed in COS cells, though at a much lower level than ras.
Ras蛋白在其羧基末端的CAAX基序处进行翻译后修饰，包括三个步骤：C被法尼基化、AAX被蛋白水解切割以及羧基甲基化。这些修饰与附近位点或多碱性区域的棕榈酰化协同作用，以靶向质膜定位。相比之下，相关的YPT/Rab蛋白定位于内膜系统的区室，可能参与指导膜运输。这些蛋白以XCC或CXC基序结尾。我们分析了裂殖酵母粟酒裂殖酵母中该亚家族成员的加工过程。我们发现在网织红细胞裂解物中进行体外翻译时，YPT1、-3和-5被香叶基香叶基化，并且当它们在体内转染的COS细胞中表达时，会掺入来自[3H]甲羟戊酸的标记。此外，香叶基香叶基化在体内对于膜结合是必需的。CXC蛋白YPT5，但两个XCC蛋白YPT1和YPT3均未在粟酒裂殖酵母和体内的COS细胞中进行羧基甲基化。然而，YPT5在能够甲基化Ras蛋白的裂解物中体外未进行羧基甲基化。当在COS细胞中表达时，YPT3可检测到棕榈酰化，尽管水平比Ras低得多。
