12-01 :: January 2012

nanotimes Research

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Video: A computer animation demonstrates the flexible dynamics – the moving parts – of human IgG antibody. 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. © LBL

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 scien- tists armed with far more powerful protein modeling tools. “We are well on our way,” says Ren.

Ren’s lab specializes in cryoEM, which examines objects frozen at -180 °C (-292 °F). A bath of liquid nitrogen flash-freezes samples so quickly that no ice crystals form. “It is amorphous, like glass,” Ren says. The protein samples are frozen on a disk the size of baby’s fingernail, filled with tiny wells 2 microns across. The disk is inserted into the microscope on a rotating support that can tilt the sample up to 140° inside a vacuum – sufficient camera angles to produ- ce a 3-D perspective. “The challenge is to isolate it from the air, and to turn it without vibrations, even

the vibrations from the bubbling of liquid nitrogen,’’ says Ren. The extremely low temperature fixes the samples and prevents them from drying out in the vacuum needed for the electron scan. It creates con- ditions favorable for imaging at much lower doses of electrons — low enough to keep a single soft protein intact while more than 100 images are taken over a one-to-two hour period.

Lei Zhang, Gang Ren: IPET and FETR: Experimental Ap- proach for Studying Molecular Structure Dynamics by Cryo-Electron Tomography of a Single-Molecule Structure, In: PLoS one, January 24, 2012, DOI:10.1371/journal. pone.0030249:

http://dx.plos.org/10.1371/journal.pone.0030249 http://www.lbl.gov http://www.youtube.com/watch?v=0t0sxDGOSkQ