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Hughson Lab Research

Structural Cell Biology

We are using biochemical and biophysical methods, particularly X-ray crystallography, to ask mechanistic questions about protein function.

Structural foundations of intracellular transport and secretion

Proteins are transported from one cellular location to another packaged within small vesicles. These vesicles bud from one compartment (for example, the endoplasmic reticulum) carrying a specific cargo which they deliver to a different compartment (for example, the Golgi apparatus) by docking and fusing with it. Many of the proteins that carry out cargo selection, budding, docking, and fusion have begun to be identified.

How intracellular traffic is controlled to bring about the biochemical architecture of eukaryotic cells is a central question in biology. To develop a molecular framework for investigating this question, we have been studying the protein machines that mediate vesicle docking and fusion. The active fusion apparatus is thought to be a complex between SNARE proteins, each anchored in one of the two membranes.

Schematic of SNARE-mediated membrane fusion.  Different SNARE proteins are illustrated in blue, red, and green.

The initial recognition between a vesicle and its membrane target, on the other hand, is mediated by large protein complexes called tethering factors. Tethering factors act upstream of SNARE complex assembly and play key roles in determining the specificity of trafficking.  Because little is known about the structures of tethering factors or the mechanism(s) by which they act, we have recently initiated biochemical and biophysical studies of these key protein complexes.

Bacterial Quorum Sensing

Cell-cell communication in bacteria is accomplished through the exchange of extracellular signalling molecules called autoinducers. This process, termed quorum sensing, allows bacterial populations to coordinate gene expression and is important, for example, in virulence and biofilm formation. Our colleague Bonnie Bassler and her lab discovered an autoinducer (AI-2) that appears to serve as a 'universal' signal for inter-species communication. The chemical identity of AI-2 has, however, proved elusive. We have recently determined the crystal structure of an AI-2 sensor protein in a complex with autoinducer. The bound ligand is a furanosyl borate diester bearing no resemblance to previously characterized autoinducers. Our findings indicate a novel biological role for boron, an element required by a number of organisms but for unknown reasons.  In collaboration with the Bassler and Semmelhack labs at Princeton, we are currently combining structural, biochemical, chemical, and genetic approaches to characterize AI-2 signaling in biology.  In a second major project, we are investigating mechanisms of intercellular communication in Vibrio cholerae, where virulence is under the control of the quorum sensing signal molecule CAI-1.

X-ray crystallographic electron density of AI-2 (blue), with the boron atom shown in yellow.  Protein side chains of the AI-2 sensor protein LuxP hydrogen bond (red dashed lines) to the ligand.





Site updated Aug 1st 2010
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