Pan Luying, Lachowicz Jake C, Paddy Isaac, Xu Yutong, Yang Qianyi, Zizola Cynthia, Milne Amy, Grove Tyler L, Pandelia Maria-Eirini
Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02453, United States.
Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, United States.
JACS Au. 2025 Apr 17;5(4):1862-1874. doi: 10.1021/jacsau.5c00090. eCollection 2025 Apr 28.
Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a metal-dependent hydrolase that plays key roles in dNTP homeostasis, antiretroviral defense, and regulation of various cancers in humans. Beyond mammals, SAMHD1 is also present in a wide range of eukaryotes, including invertebrates, plants, and human parasites. Although the specific mechanisms and biological significance of SAMHD1 in these organisms are not well understood, its functions are linked to essential processes such as photosynthesis, genome maintenance, and immune response. In this study, we bioinformatically mined the SAMHD1 superfamily and selected the ortholog from the mycorrhizal fungus as a model system for both fungal and biochemically intractable plant SAMHD1s. SAMHD1 retains the substrate promiscuity of the human enzyme but bypasses the strict requirement for allosteric activation through tetramerization, positioning it as a prototypical enzyme in which hydrolysis and allosteric regulation can be uncoupled. Its activity is selectively dependent on transition metal ions such as Mn and Fe, while Mg serves as a poor activator. Although SAMHD1 lacks several ancillary regulatory features present in human SAMHD1, its activity is differentially modulated by GTP, which acts as an allosteric activator at lower concentrations and an allosteric inhibitor at higher concentrations. These results demonstrate that metal dependence and allosteric regulation are adaptive traits that have evolved divergently among mammals, fungi, and plants, invoking alternative molecular routes for fine-tuning dNTP levels. Our findings on SAMHD1 provide a paradigm for the mechanistic diversification of SAMHD1 enzymes and offer valuable insights for dissecting the complex mechanisms of nucleotide regulation in humans.
含无菌α基序和HD结构域蛋白1（SAMHD1）是一种金属依赖性水解酶，在人类的脱氧核苷酸三磷酸（dNTP）稳态、抗逆转录病毒防御以及多种癌症的调控中发挥关键作用。除哺乳动物外，SAMHD1在包括无脊椎动物、植物和人类寄生虫在内的多种真核生物中也存在。尽管SAMHD1在这些生物体中的具体机制和生物学意义尚未完全明确，但其功能与光合作用、基因组维持和免疫反应等重要过程相关。在本研究中，我们通过生物信息学方法挖掘了SAMHD1超家族，并选择了菌根真菌中的直系同源物作为真菌和生物化学上难以处理的植物SAMHD1的模型系统。SAMHD1保留了人类酶的底物多特异性，但绕过了通过四聚化进行变构激活的严格要求，使其成为一种典型的酶，其中水解和变构调节可以解偶联。其活性选择性地依赖于过渡金属离子，如锰和铁，而镁作为较差的激活剂。尽管SAMHD1缺乏人类SAMHD1中存在的几个辅助调节特征，但其活性受到鸟苷三磷酸（GTP）的差异调节，GTP在较低浓度下作为变构激活剂，在较高浓度下作为变构抑制剂。这些结果表明，金属依赖性和变构调节是在哺乳动物、真菌和植物中 divergent 进化的适应性特征，引发了用于微调dNTP水平的替代分子途径。我们对SAMHD1的研究结果为SAMHD1酶的机制多样化提供了一个范例，并为剖析人类核苷酸调节的复杂机制提供了有价值的见解。
