The structural information of proteins is used to develop new drugs that are effective and have few side effects. Currently, single particle analysis by cryo-electron microscopy (cryo-EM) is becoming an essential tool in determining the structure of proteins for this drug discovery. However, this requires taking and averaging tens of thousands of protein particle images, all of which have been done with dedicated cryo-EM equipment. However, these devices are expensive, and the usages are limited.

In this study, we verified whether it is possible to determine the structure of proteins by utilizing general-purpose electron microscopes, which have been more installed in universities and research institutes. By optimizing the magnification, exposure conditions of the electron microscope etc., we succeeded in determining the atomic structure of apoferritin at below 3 Å (0.3 nm) resolution. The structural model of apoferritin showed the shape and orientation of the individual side chains of the amino acids in this protein. In addition, by using automatic image acquisition software, the number of images taken could be increased by about 3 times, and β-galactosidase, which is a soluble protein with lower structural symmetry, was able to determine the structure at 3.6 Å (0.36 nm) resolution.

This result shows that the structural analysis of some proteins can be performed by optimizing the imaging conditions in a general-purpose electron microscope rather than an expensive dedicated cryo-electron microscope device. It is expected that this report will further advance the structural analysis of proteins by cryo-EM single particle analysis and promote the development of safe drug discovery.

general-purpose electron microscope (left) and apoferritin structure below 3 Å resolution (right).

Collaborative Researcher

Yoko Kayama (Terabase comapy, NIPS)
Raymond N. Burton-Smith, Chihong Song, Kazuyoshi Murata (NIPS)
Takayuki Kato (Osaka University)
Naoya Terahara (Chuo University)

Funding

Collaborative Study with Terabase company