Inhibition of N-end rule-dependent proteolysis by dipeptide

在与日本宇宙开发事业团（NASDA）的合作项目中，我们发现泛素依赖的蛋白水解在航天引起的肌肉萎缩中起重要作用。在这种蛋白水解途径中，一种降解信号的基本组成部分是蛋白质的不稳定N-末端残基（N-末端规则）。有趣的是，在该系统中的蛋白质降解被抑制的二肽。在本研究中，我们研究了各种二肽对氧化应激诱导的蛋白质泛素化的抑制作用，氧化应激触发了太空中肌肉蛋白的泛素化。在大鼠成肌细胞L 6细胞用0.5毫米过氧化氢处理，许多低分子量的蛋白质被泛素化。通过微测序分析，我们确定了一个分子量为37 kDa的泛素化蛋白作为糖酵解途径中的酶。我们还发现，一些二肽，如Ala-X和Ala-Y，影响其泛素化：前者显着抑制泛素化，而后者进一步增强它。我们的研究结果表明，一些二肽可能通过调节泛素系统影响骨骼肌糖酵解。

In the joint project with National Space Development Agency of Japan (NASDA), we found that ubiquitin - dependent proteolysis plays an important role in muscle atrophy caused by spaceflight. The essential component of one degradation signal in this proteolytic pathway is a destabilizing N-terminal residue of a protein (the N-end rule). Interestingly, the protein degradation in this system is inhibited by dipeptide. In the present study, we examine suppressive effect of various dipeptides on protein - ubiquitination induced by oxidative stress, which triggers ubiquitination of muscle proteins in space. In rat myoblastic L6 cells treated with 0.5 Mm hydrogen peroxide, many proteins with low molecular masses were ubiquitinated. By a micro-sequencing analysis, we identified a ubiquitinated protein with a molecular mass of 37 kDa as an enzyme in glycolytic pathway. We also found that several dipeptides, such as Ala-X and Ala-Y, affect its ubiquitination : the former significantly suppressed the ubiquitination, while the latter further enhanced it. Our results suggest that some dipeptides could affect glycolysis in skeletal muscle by regulating the ubiquitin system.