Cryo-Electron Microscopy Technology Development

In the past decade, our lab has collected ~35,000 tomograms of more than 200 different biological specimens. The wealth of information from our group and others is wasted without a way to curate the data. In response to this need, we developed the Caltech Tomography Database, a secure, searchable repository tailored to 3-D imaging datasets. We then built the ETDB-Caltech, an open repository of more than 10,000 tomographic datasets for public use.

One major goal of our lab is to increase the throughput of cryoET imaging. A decade ago, it could take all day to collect a few tomographic tilt-series. Now, we can automatically collect a tilt-series in a few minutes, and we are currently developing even faster data collection. To facilitate high-throughput data processing, we developed an automatic processing pipeline to handle data as it comes off the microscope and perform initial analysis.

Image quality is increasing thanks to advances in cryo-EM technology. We have replaced traditional phosphor-charge-coupled devices with direct detectors capable of recording individual electron hits. We have implemented energy filters to block inelastically-scattered electrons, increasing resolution of thick biological samples. We have implemented phase plates to boost contrast, allowing data collection with less radiation damage.

One of the main difficulties in resolving a structure by cryoET is identifying it in the complicated environment of the cell. We were the first to use correlated light microscopy and cryoET of a cryopreserved bacterial cell to identify a subcellular object, and have since used it to identify several structures in vivo. Taking that a step further, we developed correlated cryogenic super-resolution light microscopy (“cryo-PALM”) and cryoET. This allows us to pinpoint the location of a fluorescently-tagged protein of interest, which we can then image at high resolution by cryoET.