Scientists at Baylor College of Medicine, the Lawrence Berkeley National Laboratory, Massachusetts Institute of Technology, and Purdue University have completed a model of unprecedented near-atomic resolution of the chemical structure of the P22 virus. The study was published online on March 7, 2017 in PNAS. The open-access article is titled “Accurate Model Annotation of a Near-Atomic Resolution Cryo-EM Map.” For nearly 30 years, the laboratory of Dr. Wah Chiu, Distinguished Service Professor and Alvin Romansky Professor of Biochemistry and Molecular Biology at Baylor and senior author of the paper, has been applying electron cryomicroscopy and computer reconstruction techniques to determine the 3-D structures of biological nanomachines, such as the P22 virus. This virus is a bacteriophage -- a type that infects bacteria, in this case Salmonella -and has been extensively studied through genetics, biochemistry, and biophysics. Nevertheless, its precise chemical structure has remained unresolved. "In 2011, we published a structure of the P22 virus that allowed us to trace out a majority of the protein backbone with certainty, but we could not visualize the fine details, such as individual, small side chains," said co-first author Corey Hryc, a graduate student in the Chiu lab. "Since then, the technology in the microscopes has improved; we have new detectors that allow us to record better- and higher-contrast images to improve the resolution of our data. In addition, we have new processing algorithms that allow us to increase our ability to resolve the structure." "The novelty of this work is that we took more than 20,000 two-dimensional individual images of the P22 virus with the electron cryomicroscope and combined them using computational protocols to produce a 3-D map with unprecedented detail," Dr. Chiu said.
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