In the very crowded inner environment of a cell, most macromolecules function in the form of complexes, many being described as “molecular machines”. To understand the machines’ structures and structural changes that occur during the working cycle, we employ cryo-EM to visualize them as “single particles” or ordered functional assemblies. The micrographs are analyzed by computational image processing to reveal the structures and conformational variations of these molecules. We then combine the structural information with data from accompanying biophysical and biochemical techniques to elucidate the mechanisms of these large macromolecular machines.

Our current research focuses on three topics:

Structure and mechanism of macromolecular complexes in RNA metabolism. We have been using electron microscopy as our major tool to study the structure and mechanism of macromolecular complexes involved in RNA metabolism, including the human RISC-loading complex (RLC) for small RNA biogenesis in RNA interference pathway, the eukaryotic exosome complex responsible for RNA degradation, the Ro-Y-RNA-PNPase complex (RYPER) in RNA quality control, and more recently, the Group II Intron RNP complex.

1. Architecture and mechanism of the RISC-loading complex (RLC) in RNA interference pathways.

2. Mechanisms and regulations of exosome-mediated RNA processing and degradation.

3. Structure and mechanism of Group II Intron RNP complex.

Structure and mechanism of interactions between cytoskeleton and membrane systems. The complex cytoskeleton systems including microtubules, actin networks and cell membranes work together in many vital physiological processes. The coordination among these systems is highly regulated and essential in cell shape and polarity definition, cell migration, cell division, and intra-cellular vesicle trafficking and so on. We study the coordination mechanisms among microtubules, actin networks, and cell membranes with cryo-EM.

The mechanism of WHAMM in coordinating cytoskeleton systems in membrane deformation.

Cryo-electron microscopy method development and application. As a group using cryo-EM as the major tool, we are devoted to new method implementation and application depending on the nature of different samples that we work on. A major goal of my laboratory is to push the technical boundary of the single particle cryo-EM to study the structure of relatively flexible and small-sized (<300kDa) asymmetric molecules and their accompanying structural changes. In this regard, we exploited new electron microscopy methods and implemented new algorithms to analyze macromolecules with the aforementioned nature.

 1. Developing new algorithms for single particle reconstruction of phase-plate cryo-EM images in the structural analysis of human Dicer (220kDa).

2. Implementing new algorithms dealing with conformational heterogeneity in single particle cryo-EM analysis.

3. Exploiting near-atomic resolution single particle reconstruction of macromolecules with small size.