Sacchi Silvia, Rabattoni Valentina, Miceli Matteo, Pollegioni Loredano
"The Protein Factory 2.0", Dipartimento di Biotecnologie e Scienze della Vita, Università degli Studi Dell'Insubria, Varese, Italy.
Front Mol Biosci. 2021 May 10;8:684934. doi: 10.3389/fmolb.2021.684934. eCollection 2021.
In the central nervous system, the flavoprotein D-amino acid oxidase is responsible for catabolizing D-serine, the main endogenous coagonist of N-methyl-D-aspartate receptor. Dysregulation of D-serine brain levels in humans has been associated with neurodegenerative and psychiatric disorders. This D-amino acid is synthesized by the enzyme serine racemase, starting from the corresponding L-enantiomer, and degraded by both serine racemase (via an elimination reaction) and the flavoenzyme D-amino acid oxidase. To shed light on the role of human D-amino acid oxidase (hDAAO) in D-serine metabolism, the structural/functional relationships of this enzyme have been investigated in depth and several strategies aimed at controlling the enzymatic activity have been identified. Here, we focused on the effect of post-translational modifications: by using a combination of structural analyses, biochemical methods, and cellular studies, we investigated whether hDAAO is subjected to nitrosylation, sulfhydration, and phosphorylation. hDAAO is S-nitrosylated and this negatively affects its activity. In contrast, the hydrogen sulfide donor NaHS seems to alter the enzyme conformation, stabilizing a species with higher affinity for the flavin adenine dinucleotide cofactor and thus positively affecting enzymatic activity. Moreover, hDAAO is phosphorylated in cerebellum; however, the protein kinase involved is still unknown. Taken together, these findings indicate that D-serine levels can be also modulated by post-translational modifications of hDAAO as also known for the D-serine synthetic enzyme serine racemase.
在中枢神经系统中，黄素蛋白D-氨基酸氧化酶负责分解代谢D-丝氨酸，它是N-甲基-D-天冬氨酸受体的主要内源性协同激动剂。人类大脑中D-丝氨酸水平的失调与神经退行性疾病和精神疾病有关。这种D-氨基酸由丝氨酸消旋酶从相应的L-对映体开始合成，并由丝氨酸消旋酶（通过消除反应）和黄素酶D-氨基酸氧化酶降解。为了阐明人类D-氨基酸氧化酶（hDAAO）在D-丝氨酸代谢中的作用，已对该酶的结构/功能关系进行了深入研究，并确定了几种控制酶活性的策略。在这里，我们重点研究了翻译后修饰的影响：通过结合结构分析、生化方法和细胞研究，我们研究了hDAAO是否会发生亚硝基化、巯基化和磷酸化。hDAAO发生了S-亚硝基化，这对其活性产生负面影响。相反，硫化氢供体硫氢化钠似乎会改变酶的构象，稳定对黄素腺嘌呤二核苷酸辅因子具有更高亲和力的一种形式，从而对酶活性产生积极影响。此外，hDAAO在小脑中会发生磷酸化；然而，所涉及的蛋白激酶仍然未知。综上所述，这些发现表明，hDAAO的翻译后修饰也可以调节D-丝氨酸水平，这与D-丝氨酸合成酶丝氨酸消旋酶的情况相同。
