CONTROL OF EUCARYOTIC MEMBRANE FUNCTION BY METHYLATION

这项建议的目的是了解生理上的 一种酶促甲基化反应出现的意义 是改变细胞内蛋白质代谢的一步。 这种无处不在的酶活性催化S- 腺苷蛋氨酸依赖的甲酯化反应 异构化和消旋化的天冬氨酸残基种类繁多 膜蛋白和胞质蛋白。功能正常的L- 天冬氨酸和L-天冬酰胺残基可自发改变 老化和/或损伤反应形成D-天冬氨酸残基和L- 异天冬氨酸氨基转移酶产物。含有这些的蛋白质 后一种残基可能不是完全起作用的，我们 有兴趣探索一种可能性，酶 这些蛋白质的甲基化可能导致它们的修复和/或 退化。由于化学物质的变质、替换或 各种大分子的修复很可能是一个主要的 生物体衰老过程中的决定因素，理解 这些反应的作用可能对我们的 关于细胞生理系统稳定性的概念 延长的时间段。 我们建议将我们的努力集中在甲基化上 人类红细胞系统中的异常蛋白质，其中 蛋白质合成的缺失简化了实验设计。 尽管之前的研究表明，类似的甲基化 反应发生在其他哺乳动物组织中，不同的 甲基化蛋白质的新陈代谢可能存在，我们将 有兴趣在非红系组织中比较这些反应。 我们在此项目期间的具体目标包括进一步推动我们的 对蛋白质羧基的酶学认识 甲基转移酶，表征特定的位点 细胞膜和胞浆蛋白的甲基化，以及 勾勒出代谢的各种可能的途径 甲基化蛋白质。我们将继续使用合成肽 作为甲基化和去甲基化反应的模型。我们的 长期目标将是了解蛋白质的功能作用 参与修复的共价修饰反应 和/或细胞蛋白质的特定降解。

The objective of this proposal is to understand the physiological significance of an enzymatic methylation reaction which appears to be a step in the metabolism of altered intracellular proteins. This ubiquitous enzymatic activity catalyzes the S- adenosylmethionine-dependent methyl esterification of isomerized and racemized aspartic acid residues in a wide variety of membrane and cytosolic proteins. Normally functional L- aspartyl and L-asparaginyl residues can be altered by spontaneous aging and/or damage reactions to form D-aspartyl residues and L- isoaspartyl transpeptidation products. Proteins containing these latter residues may not be expected to be fully functional, and we are interested in pursuing the possibility that the enzymatic methylation of these proteins may lead to their repair and/or degradation. Since the chemical deterioration, replacement, or repair of various macromolecules is likely to be a major determinant in the aging process of an organism, understanding the role of these reactions may contribute significantly to our concepts of the stability of cellular physiological systems over extended periods of time. We propose to concentrate our efforts on the methylation of abnormal proteins in the human erythrocyte system, where the absence of protein synthesis simplifies the experimental design. Although previous work has shown that similar methylation reactions occur in other mammalian tissues, differences in the metabolism of the methylated proteins may exist and we will be interested in comparing these reactions in non-erythroid tissues. Our specific goals in this project period include furthering our understanding of the enzymology of protein carboxyl methyltransferases, characterizing the specific sites of methylation on membrane and cytosolic proteins in the cell, and delineating the various possible pathways for the metabolism of methylated proteins. We will continue to use synthetic peptides as models for the methylated and demethylation reactions. Our long term goal will be to understand the functional role of protein covalent modification reactions that are involved in the repair and/or specific degradation of cellular proteins.