Electron Microscopy: A 3-D Image of an Individual Protein

Jan. 25, 2012

3-D images from a single particle (A) a series of images of an ApoA-1 protein particle, taken from different angles as indicated. A succession of four computer enhancements (projections) clarifies the signal. In the right column is the 3-D image compiled from the clarified data. B) is a close-up of the reconstructed 3-D image. C) Analysis shows how the particle structure is formed by three ApoA-1 proteins (red, green, blue noodle-like models)

3-D images from a single particle (A) a series of images of an ApoA-1 protein particle, taken from ... more

When Gang Ren whirls the controls of his cryo-electron microscope, he compares it to fine-tuning the gearshift and brakes of a racing bicycle. But this machine at the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) is a bit more complex. It costs nearly US-$ 1.5 million, operates at the frigid temperature of liquid nitrogen, and it is allowing scientists to see what no one has seen before.

At the Molecular Foundry, Berkeley Lab's acclaimed nanotechnology research center, Ren has pushed his Zeiss Libra 120 Cryo-Tem microscope to resolutions never envisioned by its German manufacturers, producing detailed snapshots of individual molecules. He and his colleague Lei Zhang are reporting the first 3-D images of an individual protein ever obtained with enough clarity to determine its structure.

Scientists routinely create models of proteins using X-ray diffraction, nuclear magnetic resonance, and conventional cryo-electron microscope (cryoEM) imaging. But these models require computer "averaging" of data from analysis of thousands, or even millions of like molecules, because it is so difficult to resolve the features of a single particle. Ren and Zhang have done just that, generating detailed models using electron microscopic images of a single protein.
He calls his technique "individual-particle electron tomography," or IPET. The work is described in the open-source scientific journal Plos One.

A computer animation demonstrates the flexible dynamics - the moving parts - of human IgG antibody (see video). 3-D images of two individual antibody particles (gray) were generated using EM tomography with IPET. The demonstration shows how the same molecular chains (red, orange, and green noodle-like models) of antibody particle #1 can fit precisely into particle #2, which was found under the microscope in an entirely different pose.

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Electron Microscopy: A 3-D Image of an Individual Protein

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