Research Focus  

One area of research in the lab centers on the mechanisms of eukaryotic gene regulation, including the molecular basis of signal transduction, transcription regulation and epigenetic control of chromosome structure and conformation. Specific projects in this area include structural and functional studies of NFAT, MEF2, FOXP3, and several transcription factors implicated in stem cell pluripotency and lineage-specification. Another area of research focuses on the structure and function of nicotinic acetylcholine receptors (nAChR) and other ligand-gated ion channels (LGICs) in neuronal signaling. We use X-ray crystallography and other biochemical methods to characterize molecular complexes of interest. Based on the structures, we use mutagenesis to further analyze the functions of these complexes in vitro and in vivo.

An important aspect of our research is to combine structural biology and chemical design to study the function of bio-macromolecular complexes. We seek to develop new biochemical techniques and cell permeable small molecules for studying the function of protein complexes in vivo. The broad goal of our studies is to understand how protein-protein interactions control the specificity of biological processes inside cells. Through this knowledge we hope to gain the ability to control specific protein-protein interactions for developing research tools and therapeutic drugs.
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Images of Research Highlights  

Combinatorial gene regulation by the assembly of distinct NFAT Complexes

We have been carrying out systematic structural and functional studies of distinct NFAT complexes in collaboration with Dr. Anjana Rao¡'s lab at Harvard Medical School. These studies have shown that NFAT and the forkhead transcription factor FOXP3 bind DNA cooperatively to regulate the function of regulatory T cells (Cell, 2006, 126, 375-387). We have previously shown that NFAT controls effector immune responses by forming cooperative NFAT/Fos-Jun/DNA complexes at regulatory elements of activation-associated genes (Nature, 1998, 392, 42-48). Thus, by switching transcriptional partners, NFAT converts the acute T cell activation program into the suppressor program of regulatory T cells.

Crystal Structure of the NFAT5 (TonEBP) bound to DNA

The butterfly-like structure of the NFAT5 dimer bears a strong resemblance to NF-kB, a well-known transcription factor in stress responses. The structural similarity provides a direct link between NFAT and the classical Rel/ NF-kB proteins. The two NFAT5 monomers contact each other on opposite sides of the DNA, presenting the first example of DNA encirclement by a sequence-specific transcription factor. This work has been published in Nature Structural Biology (2002, 9, 90-4).

Sequence-specific recruitment of transcription co-regulators by MEF2 bound to DNA

This study provides the first atomic view of the recruitment of a transcriptional co-repressor (Cabin1) by a DNA-bound, sequence-specific transcription factor MEF2. The structure of the Cabin1/MEF2/DNA complex provides a framework for further studying the recruiting mechanism of class II histone deacetylases (HDACs) and transcription coactivator p300 by MEF2 in muscle and neuronal cells. Both class II HDAC and p300 are key regulator of cardiac gene expression in heart. This work has been published in Nature (2003, 422, 70-4).

Structural studies of the host factor NFAT1 bound to HIV-1 LTR

This work illustrates how NFAT1, despite being a monomer in solution, can bind cooperatively as a dimer to the highly conserved kappa-B site from the HIV-1 LTR. This structure provides a strong support for the functional observations that NFAT1 can activate specific subsets of host and viral genes from kappa-B-like DNA sites. Like the NFAT5 (TonEBP)/DNA complex, the two NFAT1 monomers form a complete circle around the DNA. However, the dimer interface formed by the C-terminal domain is asymmetric and significantly different from the symmetric dimer interface seen in NFAT5 and other Rel family proteins. This work has been published in Nature Structural Biology for publications (2003, 10, 800-806).

Structural studies of nicotinic acetylcholine receptors

A model of sugar-mediated gating mechanism of nicotine receptors
One component of the nicotinic acetylcholine receptor (nAChR) pentamer, the alpha1 subunit, is highlighted in red (depicted in ribbon). Other subunits are colored in gray (two are visible in this view). When nicotine binds to a site on nAChR (indicated by arrow #1), which is occupied by a snake toxin (alpha-bungarotoxin, colored in yellow) in this structure, the surrounding protein structure contracts. This contraction will pull the sugar chain upward (depicted in clustered spheres, arrow #2). The other end of the sugar chain is attached to a loop (a.k.a. Cys-loop) engaged with the membrane helices (referred to as the hinge in the figure, arrow #3). The upward move of the sugar chain, which is facilitated by buried water molecules (blue spheres between the two beta sheets), would trigger motions of the trans-membrane helices and the opening of the ion gate (arrow #4). The ions (green spheres) will subsequently flow from outside of the cell to the inside, thus completing a step of chemical transmission of the electrical signal between neurons or between neurons and their target cells. (Dellisanti et al., Nature Neuroscience, August, 2007)