Biological macromolecules adopt complicated three-dimensional (3D) structures that are critical to their function. We want to learn how these complicated structures help macromolecules perform particular tasks. To do this we use a visualization technique called electron cryomicroscopy (cryo-EM), which involves firing a beam of high-energy electrons at a biological sample at cryogenic temperatures. Some of these electrons interact with the sample and when recorded form a 2D image of the sample. A 3D density map can then be formed from a series of these 2D images. In recent years the quality of these maps has improved rapidly and often have sufficient detail (resolution) to build an atomic model of the structure. This “resolution revolution” is the result of better microscopes, advances in electron detection, and new mathematical models for interpreting the raw images.

Cryo-EM has made the impossible possible. We can now visualize macromolecules that are structurally heterogeneous, produced at low yield, and, perhaps most excitingly, directly in their native environment.

Structural and Functional Studies of the Axoneme

Central to all cilia is the axoneme, one of the most geometrically complex and structurally conserved macromolecular machines found in nature. Using high-resolution cryo-EM techniques we are beginning to resolve this beautiful structure in atomic detail. Recently, we have determined structures of ciliary doublet microtubulesradial spoke complexesmicrotubule-bound axonemal dyneins, and the central apparatus from the model organism Chlamydomonas reinhardtii. These studies have revealed new insights into the principles that guide the assembly of the axoneme and the mechanisms that regulate ciliary motility. This project is an ongoing collaboration with Dr. Rui Zhang and Dr. Susan Dutcher at Washington University in St. Louis. Using methods developed for studying Chlamydomonas axonemes, we are now beginning to explore the mammalian structures, with the aim to better understand human ciliopathies.

Molecular Transport in the Cilium

One of our long-term goals is to understand transport mechanisms in the cilium. We are particularly interested in the interplay between microtubules, motor proteins, adaptor complexes and their cargoes, and the role of these processes in signaling pathways. To do this we use a combination of structural, biophysical and biochemical techniques with an emphasis on high-resolution electron microscopy. An example of our recent work in this area is the cryo-EM structure of the mammalian BBSome complex, which transports transmembrane proteins in the cilium.

Methods for interpreting cryo-EM maps

We are also interested in developing new methods to accelerate and improve cryo-EM structure determination. In particular how we can improve the interpretation of cryo-EM density maps with all-atom models and make these models as accurate as possible.

Some useful tools that we helped develop for cryo-EM can be found here.