Max Planck researchers from Dortmund reveal the first-ever detailed structure of the bacterial toxin Mcf1
來自德國多特蒙德市，馬克斯普朗克研究所的研究人員們，首次揭露細菌毒素Mcf1的細部結構。
During infection insect-killing bacteria typically release toxins to slay their hosts. The bacterium Photorhabdus luminescens, for example, pumps insect larvae full of the lethal ‘Makes caterpillars floppy 1’ (Mcf1) toxin, leading them to first become droopy and then dead.
於感染期間，殺死昆蟲的細菌，通常釋放毒素，來殺死其宿主。譬如，發光桿菌(Photorhabdus luminescens)將非常致命之‘使毛毛蟲沒精神1’(Mcf1)的毒素注入昆蟲幼蟲中，導致它們首先變得喪失活力，然後死亡。
However, it has so far been a mystery how Mcf1 unfolds its devastating effect. Researchers at the Max Planck Institute of Molecular Physiology in Dortmund, successfully analyzed the Mcf1 structure, allowing them to propose a molecular mechanism of the toxin’s action.
不過，迄今為止，Mcf1如何展現其破壞性作用，一直是個謎。於多特蒙德市，馬克斯普朗克分子生理學研究所的研究人員們，成功分析了使他們得以提出，Mcf1該毒素作用之分子機制的結構。
Understanding how bacterial toxins perform their deadly task in such detail is very useful for engineering novel biopesticides, thereby reducing the use of barely specific chemical agents with harmful side effects for the ecosystem.
就設計新型生物殺蟲劑而言，如此詳細瞭解細菌毒素，如何執行其致命任務，是非常有用的。從而減少對生態體系，具有害副作用、幾乎沒有特效之化學製劑的使用。
圖1. Mcf1類似一隻，頭部具有多種有毒之有效載荷，而尾部區域能附著於標的細胞的海馬。
Mcf1 resembles a seahorse with a head containing several toxic payloads, while the tail region can attach to target cells.
“Ours is the first-ever structural study of this toxin,” explains Alexander Belyy, first author of the study. The challenge of the project, which took a decade of work, lay in the fact that the protein is relatively large and composed of multiple modules, each devoted to a specific function.
該項研究首要撰文人，Alexander Belyy解釋：「我們的研究，是該種毒素的首次結構研究。」該項花費十年的研究課題，挑戰在於，該蛋白質相對上是大的，且由每一模組專注於特定功能之多個模組組成的事實。」
“The use of our cutting-edge cryo-EM equipment and computational power was instrumental to resolve this structure,” says Stefan Raunser, director at the Max Planck Institute for Molecular Physiology.
馬克斯普朗克分子生理學研究所所長，Stefan Raunser宣稱：「我們尖端的低溫電子顯微鏡檢查(cryo-EM：cryogenic Electron Microscopy)設備及計算能力的使用，有助於解析此結構。」
Cryo-EM allows researchers to obtain 3D images of a protein at near-atomic resolution, in this case at 3.6 Ångstrom – meaning that details 200,000 times smaller than the width of a human hair could be observed.
Cryo-EM使研究人員們得以，以接近原子的解析度，在此事例中以3.6埃，獲得蛋白質的3D影像。這意味著，能觀察比人類頭髮寬度，小20萬倍的細部。
The scientists were able to show that the structure of Mcf1 resembles a seahorse. Parts of the "head region" are toxic. These are released from the head by enzymes as soon as it enters the cell. The tail region can adhere to target cells.
此些科學家們能證實，Mcf1的結構類似一隻海馬。"頭部區域"的部分有毒。一進入細胞中，它們就精由酵素從頭部釋出。尾部區域能附著於標的細胞上。
After the toxin is released by bacteria in the host insect, three domains in its tail region identify and bind to the target cell’s membrane. Another domain of the tail then transfers the head across the membrane into the cell’s cytoplasm.
於宿主昆蟲中，該種毒素由細菌釋放後。於其尾部區域的三個結構域，辨識並結合於標的細胞的細胞膜上。然後，尾部的另一個結構域，將頭部轉移越過細胞膜，進入細胞的細胞質中。
Once inside, the head interacts with local proteins to stimulate the release of two toxic payloads. These deadly modules disrupt the activity of essential proteins in the cell, leading to its death – and ultimately to the death of the entire insect within 24 hours of intoxication.
一旦進入內部，頭部與鄰近的蛋白質交互作用，來刺激兩種有毒之有效載荷的釋放。
圖2. 在毒素與宿主細胞表面上，迄今為止未知的受體結合後，毒素被內吞。該胞內體的酸化，於長600個氨基酸的遞送區域內觸發，於標的細胞內形成一個小孔，並使毒素頭部區域易位之構造形態的改變。在易位、一系列蛋白水解反應及裂解後。Mcf1有毒之有效載荷被釋放，這會損害重要的生理途徑，最終導致細胞死亡。
After binding of the toxin to as yet unknown receptors on the surface of the host cell, the toxin is endocytosed. Acidification of the endosome triggers a conformational change inside the 600 amino acid-long delivery region, which forms a pore and translocates the head region of the toxin inside the target cell. After translocation, a series of proteolysis reactions and cleavages, Mcf1 toxic payloads are released, which impair essential physiological pathways ultimately leading to cell death.
Intriguingly, the researchers found that the modular structure of the tail and the initial steps of Mcf1 intoxication are highly similar to toxins from Clostridioides difficile, a human pathogen responsible for more than 120,000 hospitalizations in Europe annually.
引人好奇的是，此些研究人員發現，尾部的模組化結構及Mcf1中毒的初始步驟，高度類似來自一種，每年於歐洲導致超過12萬人住院之人類病原體，困難梭狀桿菌(Clostridioides difficile)的毒素。
"Our study, which was originally aimed at improving biopesticides, will also have an impact on the understanding of human diseases," adds Philipp Heilen, co-first author of the study.
該項研究的首要合撰人，Philipp Heilen附言：「我們原本旨在改善生物殺蟲劑的研究，也會具有對瞭解人類疾病的影響。」
Looking forward, the MPI scientists want to elucidate in molecular detail how the toxic payloads of Mcf1 lead to cell death. “This new knowledge also enables engineering of highly specific insecticidal toxins,” says Stefan Raunser hinting at another future direction of research: creating new toxin variants useful for insect control.
展望未來，此些馬克斯普朗克研究所的科學家們，想從分子細部闡明，Mcf1 有毒的有效載荷，如何導致細胞死亡。暗示了，未來另一個研究方向(也就是，創造對控制昆蟲有用之新毒素變體)的Stefan Raunser宣稱：「此新知識也使得能設計，高度有效之殺蟲用的毒素。」
網址：https://www.mpg.de/21490354/0131-moph-identify-engage-assassinate-how-seahorse-like-toxins-kill-insects-151445-x?c=2249
翻譯：許東榮
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