中文摘要：噬菌体T3的S-腺苷蛋氨酸裂解酶（SAMase）降解宿主大肠杆菌细胞内SAM，从而使参与过多细胞功能（包括DNA甲基化）的关键代谢物失活。SAMase是感染表达的第一种病毒蛋白，其活性可防止T3基因组甲基化。保持噬菌体基因组处于完全非甲基化状态对感染策略有着深远的影响，它允许T3从正常生长条件下的裂解性感染转变为葡萄糖饥饿条件下的短暂温和感染。利用单粒子低温电子显微镜（cryoEM）和生化分析，证明SAMase发挥作用不仅可以通过降解SAM，还可以通过与宿主产生SAM的酶，即蛋氨酸s-腺苷转移酶（MAT）相互作用并有效抑制其功能来实现。具体地说，SAMase将大肠杆菌MAT的开放式头尾组装成一种不常见的线性丝状结构，其中相邻的MAT四聚体由两个SAMase二聚体连接。分子动力学模拟和正常模式分析表明，MAT四聚体在丝状体内的包封导致MAT活性的变构抑制，这是由于向低频、高振幅活性位点变形模式的转变。活性位点残基之间不相关运动的放大削弱了MAT的底物结合亲和力，从而出现功能丧失。据此提出SAMase具有SAM降解酶和MAT活性抑制剂的双重功能，以实现细胞内SAM的有效消耗。
  重点：根据特定的代谢线索将酶自组装成丝状结构是近年来出现的一种广泛的代谢调节策略。许多情况下，代谢酶的丝状化是应对饥饿的反应，并导致功能失活。本文报道了噬菌体T3通过一种类似的策略来调节宿主大肠杆菌细胞的代谢：通过噬菌体介导的聚合使中心代谢酶沉默。该结果指出了一种有趣的可能性，即病毒诱导的宿主代谢酶聚合是病毒通过代谢重组并抑制感染细胞的一种常见机制。
外文摘要：S-Adenosylmethionine lyase (SAMase) of bacteriophage T3 degrades the intracellular SAM pools of the host Escherichia coli cells, thereby inactivating a crucial metabolite involved in a plethora of cellular functions, including DNA methylation. SAMase is the first viral protein expressed upon infection, and its activity prevents methylation of the T3 genome. Maintenance of the phage genome in a fully unmethylated state has a profound effect on the infection strategy. It allows T3 to shift from a lytic infection under normal growth conditions to a transient lysogenic infection under glucose starvation. Using single-particle cryoelectron microscopy (cryoEM) and biochemical assays, we demonstrate that SAMase performs its function by not only degrading SAM but also by interacting with and efficiently inhibiting the host's methionine S-adenosyltransferase (MAT), the enzyme that produces SAM. Specifically, SAMase triggers open-ended head-to-tail assembly of E. coli MAT into an unusual linear filamentous structure in which adjacent MAT tetramers are joined by two SAMase dimers. Molecular dynamics simulations together with normal mode analyses suggest that the entrapment of MAT tetramers within filaments leads to an allosteric inhibition of MAT activity due to a shift to low-frequency, high-amplitude active-site-deforming modes. The amplification of uncorrelated motions between active-site residues weakens MAT's substrate binding affinity, providing a possible explanation for the observed loss of function. We propose that the dual function of SAMase as an enzyme that degrades SAM and as an inhibitor of MAT activity has emerged to achieve an efficient depletion of the intracellular SAM pools.
  IMPORTANCE Self-assembly of enzymes into filamentous structures in response to specific metabolic cues has recently emerged as a widespread strategy of metabolic regulation. In many instances, filamentation of metabolic enzymes occurs in response to starvation and leads to functional inactivation. Here, we report that bacteriophage T3 modulates the metabolism of the host E. coli cells by recruiting a similar strategy: silencing a central metabolic enzyme by subjecting it to phage-mediated polymerization. This observation points to an intriguing possibility that virus-induced polymerization of the host metabolic enzymes is a common mechanism implemented by viruses to metabolically reprogram and subdue infected cells.
外文关键词：enzyme filamentation；metabolic regulation；virus-host interaction；cryoEM; molecular dynamics (MD) simulations；bacteriophage T3；SAMase
作者：Simon-Baram, H；Kleiner, D；Shmulevich, F；Zarivach, R；Zalk, R；Tang, HY；Ding, F；Bershtein, S
作者单位：Ben Gurion Univ Negev；Clemson Univ
期刊名称：MBIO
期刊影响因子：4.778
出版年份：2021
出版刊次：4
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