The Pathways Traveled: Structural Studies of Virus Assembly

Speaker: Dr. Elizabeth Wright
Department:
Department of Pediatrics, Emory University
Subject: The Pathways Traveled: Structural Studies of Virus Assembly
Location: A1.100 TU Delft
Date: 19-05-2017

Author: Kristian Blom

On the 19th of May I visited a BN colloquium given by Elizabeth Wright, principal investigator at Emory University. The Wright lab is interested in the use of cryo-electron microscopy (cryo-EM) and molecular biology approaches to explore the three dimensional structures of viruses and cells. The goal is to use this information to aid in the development of novel antimicrobials, therapeutics, and vaccines.

Dr. Wright started by mentioning the benefits and methods in cryo-EM. One of the benefits is that samples stay in their ‘native’ state because all the molecules within the sample are frozen and thus do not move over time. The other benefit, which I think is even better than the first, is that with conventional cryo-EM specimen preparation artifacts are eliminated. While I’m writing I now realize that the cause of this benefit wasn’t mentioned during the talk, but I think it has to do with the cooling of the sample.

Within the realm of cryo-EM, there are different methods one can use to analyze your sample. The most extensively used methods are single particle analysis, electron crystallography, helical reconstruction and tomography. The latter method is imaging by sections. From these sections it is possible to make a 3D image by stacking the individual 2D images. During the talk dr. Wright showed us one example of a 3D image constructed by cryo-EM tomography.

After a short review of the different methods we moved to the recent advances in cryo-EM. These advances can be separated in three different areas: Sample preparation, data collection and data processing. Especially the data collection part has made some big improvement in 2008, when Direct-Electron introduced the large-format Direct Detection Device (DDD®). In traditional transmission electron microscopy (cry-TEM) cameras use a so-called scintillator. This is a material that produces a flash of light by the passage of a particle through it. For cryo-TEM this particle is an electron that causes a photon to be emitted by the scintillator to the CCD sensor. In contrast, the DDD directly detects image-forming electrons in the microscope without the use of a scintillator. This direct electron sensing results in better resolution, signal-to-noise ratio and sensitivity. The data processing improvements do mainly come from faster computing, better algorithms and auto-segmentation.

Figure 1: The difference between traditional transmission electron data collection and DDD data collection. Image from: http://www.directelectron.com/products/de-series

The second part of the talk was devoted to the current studies of the Wright lab. Besides the research, there is also a big interest to the technological developments of cryo-EM. One of the recent innovations is the correlation of fluorescence microscopy with electron microscopy. This allows one to improve the resolution and identify certain parts of the sample by staining them with a specific fluorophore.

To be honest, I didn’t found the talk that interesting. The slides that dr. Wright used during her talk were overcrowded with text and sometimes lacking important information. Therefore it was quite hard for me to keep my focus. Every time I was halfway through reading one slide, dr. Wright already went to the next slide.  Also I couldn’t found any structure in her presentation, and that is even more annoying for me because I always need some structure if I want to understand the complete picture of the talk. What I do like about here presentation is that she knew a lot about her field of research. All the questions she got from the audience were answered in a very nice way.

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