Graduate School of Biomedical Science and Engineering, Hanyang University, Seoul, South Korea.
Department of Pharmacology, College of Medicine, Hanyang University, Seoul, South Korea.
Sci Rep. 2022 Aug 20;12(1):14243. doi: 10.1038/s41598-022-18656-0.
Phenylalanine hydroxylase (PAH) is a key enzyme in mammals that maintains the phenylalanine (Phe) concentration at an appropriate physiological level. Some genetic mutations in the PAH gene lead to destabilization of the PAH enzyme, leading to phenylketonuria (PKU). Destabilized PAH variants can have a certain amount of residual enzymatic activity that is sufficient for metabolism of Phe. However, accelerated degradation of those variants can lead to insufficient amounts of cellular PAH protein. The optimal protein level of PAH in cells is regulated by a balancing act between E3 ligases and deubiquitinating enzymes (DUBs). In this work, we analyzed the protein expression and stability of two PKU-linked PAH protein variants, R241C and R243Q, prevalent in the Asian population. We found that the tested PAH variants were highly ubiquitinated and thus targeted for rapid protein degradation. We demonstrated that USP19, a DUB that interacts with both PAH variants, plays a regulatory role by extending their half-lives. The deubiquitinating activity of USP19 prevents protein degradation and increases the abundance of both PAH protein variants. Thus, our study reveals a novel mechanism by which deubiquitinating activity of USP19 extends the residual enzymatic activity of PAH variants.
苯丙氨酸羟化酶（PAH）是哺乳动物中维持苯丙氨酸（Phe）浓度在适当生理水平的关键酶。PAH 基因中的一些基因突变导致 PAH 酶的不稳定性，从而导致苯丙酮尿症（PKU）。不稳定的 PAH 变体具有一定量的残留酶活性，足以代谢 Phe。然而，这些变体的加速降解会导致细胞内 PAH 蛋白的含量不足。细胞中 PAH 的最佳蛋白水平通过 E3 连接酶和去泛素化酶（DUBs）之间的平衡作用来调节。在这项工作中，我们分析了两种在亚洲人群中普遍存在的与 PKU 相关的 PAH 蛋白变体 R241C 和 R243Q 的蛋白表达和稳定性。我们发现，测试的 PAH 变体高度泛素化，因此被靶向快速蛋白降解。我们证明了 USP19，一种与两种 PAH 变体相互作用的 DUB，通过延长它们的半衰期发挥调节作用。USP19 的去泛素化活性可防止蛋白降解并增加两种 PAH 蛋白变体的丰度。因此，我们的研究揭示了 USP19 的去泛素化活性延长 PAH 变体残留酶活性的新机制。
