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 $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. Today, 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 January 24 issue of PLoS One, the open-source scientific journal, in an article entitled “IPET and FETR: Experimental Approach for Studying Molecular Structure Dynamics by Cryo-Electron Tomography of a Single-Molecule Structure.”
The 3-D images reported in the paper include those of a single IgG antibody and apolipoprotein A-1 (ApoA-1), a protein involved in human metabolism. Ren’s goal is to produce individual 3-D images of medically significant proteins, such as HDL— the heart-protective “good cholesterol” whose structure has eluded the efforts of legions of scientists armed with far more powerful protein modeling tools. “We are well on our way,” says Ren.