美国亚利桑那州立大学生物设计研究所的约翰·查普特和他的同事，将实验室制造的人工合成蛋白质（DX）植入大肠杆菌细胞，发现DX蛋白质能与细胞内的ATP分子结合，使细胞分裂停止，但细胞仍在继续生长。该研究对于了解能躲避抗生素的病原体行为提供了新方法。相关研究成果刊登在《美国化学学会化学生物学》杂志网站上。
“如果你把一个在试管中创造出来的蛋白质植入细胞内，结果蛋白质在细胞内发生了作用，”查普特说道，“你觉得细胞认识它吗？细胞是咀嚼它，还是把它吐出来？”在这个值得探索的合成生物学新领域，这一发现将会使新药物的研发取得进展。
“ATP是生命的能量货币，”查普特说，在生物系统的反应中，ATP的磷酸二酯键结合需要一定的能量来驱动。DX蛋白质的结合消耗了细胞内ATP的能量，破坏了细胞正常的新陈代谢活动，阻止了细胞分裂，但细胞们仍在继续成长。
大肠杆菌暴露于DX蛋白质后，由通常的球形发展成细长的丝状。在丝状的细菌中，密集的细胞内脂质结构被划分开，形成了有相同长度的细胞，研究人员将这种此前未曾出现过的不寻常结构称为内在脂质体。
“这些致密的脂质结构正在形成非常有规律的区域，它们沿着丝状细胞逐渐形成，它们看起来像是一种防御机制，使细胞自我划分。”查普特说道。这一独特适应过程，从未在细菌细胞中观察到，同时它也是唯一出现在单细胞有机体中。合成蛋白质DX并不是一件容易事，它需要精心的模仿自然状态下蛋白质折叠的特性，并能够与关键代谢产物ATP相结合。
科学家们接下来将研究，当这些细胞遇到新情况时，它们会如何回应。例如细胞对于一个不熟悉的合成蛋白质，它们会如何应对。该研究还指出，许多传染性病原体依靠处于休眠状态（类似于DX暴露大肠杆菌中观察到的可生存但不可培养状态），躲避抗生素的检测。这一发现，对于研究这些病原体的行为提供了一个更好的方法。此外，对于生物体极其重要的ATP，抑制其作用可为防治疾病提供另一种途径。(生物谷Bioon.com)
DOI: 10.1021/cb3004786
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ATP Sequestration by a Synthetic ATP-Binding Protein Leads to Novel Phenotypic Changes in Escherichia coli
Shaleen B. Korch , Joshua M. Stomel †§, Megan A. León †, Matt A. Hamada , Christine R. Stevenson †,Brent W. Simpson †, Sunil K. Gujulla †, and John C. Chaput *†‡
Artificial proteins that bind key metabolites with high affinity and specificity hold great promise as new tools in synthetic biology, but little has been done to create such molecules and examine their effects on living cells. Experiments of this kind have the potential to expand our understanding of cellular systems, as certain phenotypes may be physically realistic but not yet observed in nature. Here, we examine the physiology and morphology of a population of Escherichia coli as they respond to a genetically encoded, non-biological ATP-binding protein. Unlike natural ATP-dependent proteins, which transiently bind ATP during metabolic transformations, the synthetic protein DX depletes the concentration of intracellular ATP and ADP by a mechanism of protein-mediated ligand sequestration. The resulting ATP/ADP imbalance leads to an adaptive response in which a large population of bacilli cells transition to a filamentous state with dense lipid structures that segregate the cells into compartmentalized units. A wide range of biochemical and microscopy techniques extensively characterized these novel lipid structures, which we have termed endoliposomes. We show that endoliposomes adopt well-defined box-like structures that span the full width of the cell but exclude the synthetic protein DX. We further show that prolonged DX exposure causes a large fraction of the population to enter a viable-but-non-culturable state that is not easily reversed. Both phenotypes correlate with strong intracellular changes in ATP and ADP concentration. We suggest that artificial proteins, such as DX, could be used to control and regulate specific targets in metabolic pathways.
