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原文见：http://web./newsoffice/2010/micro-peptides-0315.html Zooming in on cells——New microscopy technique offers close-up, real-time view of how proteins kill bacteria. by Anne Trafton新的显微技术提供了蛋白质如何杀死细菌的近景即时影像 这张图片是大肠杆菌被抗菌肽CM15处理后的原子力显微镜照片，抗菌肽已经开始破坏细菌的细胞壁。This image, taken with atomic force microscopy, shows E. coli bacteria after they have been exposed to the antimicrobial peptide CM15. The peptides have begun destroying the bacteria’s cell walls. Image: Georg Fantner
二十多年来，科学家研究一种潜在的新方法来治疗细菌感染，即使用天然蛋白质——抗微生物肽（antimicrobial peptides, AMPs）在细菌的细胞膜上穿洞来杀死细菌。如今，MIT的科学家记录了第一张即时显微影像，显示抗微生物肽在活细菌上的致命效果。For two decades, scientists have been pursuing a potential new way to treat bacterial infections, using naturally occurring proteins known as antimicrobial peptides (AMPs) that kill bacteria by poking holes in their cell membranes. Now, MIT scientists have recorded the first real-time microscopic images showing the deadly effects of AMPs in live bacteria.
由MIT的Angela Belcher教授带领的研究小组使用一种经过调整的高速原子力显微镜来拍摄细菌的即时影像。他们的方法刊登在3月14日出版的Nature Nanotechnology上，第一次使用高分辨率图像来记录活细胞的快速变化。Researchers led by MIT Professor Angela Belcher modified an existing, extremely sensitive technique known as high-speed atomic force microscopy (AFM) to allow them to image the bacteria in real time. Their method, described in the March 14 online edition of Nature Nanotechnology, represents the first way to study living cells using high-resolution images recorded in rapid succession.
Using this type of high-speed AFM could allow scientists to study how cells respond to other drugs and to viral infection, says Belcher, the Germeshausen Professor of Materials Science and Engineering and Biological Engineering and a member of the Koch Institute for Integrative Cancer Research at MIT.
It could also be useful in studying cell death in mammalian cells, such as the nerve cell death that occurs in Alzheimer’s patients, says Paul Hansma, a physics professor at the University of California at Santa Barbara who has been developing AFM technology for 20 years. “This paper is a highly significant advance in the state-of-the-art imaging of cellular processes,” says Hansma, who was not involved in the research.
1986年发明的高速原子力显微镜广泛用于纳米材料的显微照相。它的分辨率是5nm，和其它电镜类似，但是它并不象其它电镜那样需要真空，因此可以用于活细胞样品。然而，传统的原子力显微镜需要几分钟来成像，因此不能用来记录快速发生的生命现象。High speed Atomic force microscopy, invented in 1986, is widely used to image nanoscale materials. Its resolution (about 5 nanometers) is comparable to that of electron microscopy, but unlike electron microscopy, it does not require a vacuum and thus can be used with living samples. However, traditional AFM requires several minutes to produce one image, so it cannot record a sequence of rapidly occurring events.
In recent years, scientists have developed high-speed AFM techniques, but haven’t optimized them for living cells. That’s what the MIT team set out to do, building on the experience of lead author Georg Fantner, a postdoctoral associate in Belcher’s lab who had worked on high-speed AFM at the University of California at Santa Barbara.
原子力显微镜是使用一个装有探针的悬挂臂来“感觉”样品的表面。当探针在样品表面滑动的时候，探针和样品表面之间的力可以被测量，从而揭示表面的形状。MIT团队使用比常规的原子力显微镜小1000倍的的悬挂臂，使得他们可以增加成像速度而不损伤细菌。Atomic force microscopy makes use of a cantilever equipped with a probe tip that “feels” the surface of a sample. Forces between the tip and the sample can be measured as the probe moves across the sample, revealing the shape of the surface. The MIT team used a cantilever about 1,000 times smaller than those normally used for AFM, which enabled them to increase the imaging speed without harming the bacteria.
测量可以在液体环境下进行，这也是保持细菌活性的要素之一。The measurements are performed in a liquid environment, another critical factor in keeping the bacteria alive.
使用这个新装置，研究团队可以每13秒钟记录抗菌肽CM15处理后的细菌影像，一直持续几分钟。他们发现抗菌肽引起细胞的死亡是一个两步过程：一个短的潜伏时期，然后是迅速的“处决”。他们惊讶地发现潜伏时期从13-80秒钟不等。With the new setup, the team was able to take images every 13 seconds over a period of several minutes following treatment with an AMP known as CM15. They found that AMP-induced cell death appears to be a two-step process: a short incubation period followed by a rapid “execution.” They were surprised to see that the onset of the incubation period varied from 13 to 80 seconds.
“Not all of the cells started dying at the exact same time, even though they were genetically identical and were exposed to the peptide at the same time,” says Roberto Barbero, a graduate student in biological engineering and an author of the paper.
Most AMPs act by puncturing bacterial cell membranes, which destroys the delicate equilibrium between the bacterium and its environment. Others appear to target machinery inside the cell. There has been a great deal of interest in developing AMPs as drugs that could supplement or replace traditional antibiotics, but none have been approved yet.
Until a few years ago, it was thought that bacteria could not become resistant to AMPS, but recent studies have shown that they can. The new MIT work could help researchers understand how that resistance develops.
The research was funded by an Erwin-Schrodinger Fellowship, the National Institutes of Health, Army Research Office and Austrian Research Promotion Agency. |
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