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Research Goals.
Our research seeks to deliniate the structure->activity->function algorithm as it applies to proteases and their inhibitors. Our laboratory has very broad interests in principles of proteolysis in humans, and we take multi-pronged approaches to research on proteases and their inhibitors.

Apoptosis
In one approach we apply basic biochemical knowledge to investigate newly emerging principles of proteolysis in human systems. This research is currently directed at dissecting the proteolytic components of the intracellular pathway that leads to apoptotic cell death. Programmed cell death monitors the growth of new cells and the elimination of old ones. This program contains a number of proteolytic steps that are essential for efficient execution of the death pathway. Thus the proteases of the pathway - the caspases - are involved in the normal maintenance of correct cell number, and are therefore implicated in a number of pathologic and physiologic conditions. Using the techniques of protein chemistry, enzymology, crystallography, and recombinant DNA methodologies, we analyze the basic mechanism utilized by the caspases to promote cell death pathways, and the mechanisms and specificity of the natural inhibitors that control them.

Cell Signaling
Modification of proteins by the small ubiquitin-like modifier SUMO is a dynamic and reversible process.  The SUMO cycle begins when SUMO precursors are processed to remove short C-terminal extensions, thereby uncapping the C-terminal Gly-Gly motif that is essential for conjugation.  SUMO ligases conjugate the protein, via its C-terminal carboxylate, to the side-chain lysine of target proteins to generate an isopeptide linkage.  Eventually, SUMO is removed intact from its substrate SUMOylated proteins, and so the SUMOylation/deSUMOylation cycle regulates SUMOs function.  A group of proteases known as SENPs are involved in both the activation of SUMO precursors (endopeptidase cleavage) and deconjugation of the targets (isopeptidase cleavage).  Our laboratory is currently involved in projects to define the mechanisms that mediate the regulation of SENP activity and access to their natural substrates.

Technology Development
The principle of proteolysis in vivo is to instigate irreversible changes to a set of protein substrates that alters their function, and generates the required biological event. The sum total of the proteases and their target substrates operating in a physiologic pathway therefore defines the global event. Consequently, the identity of the substrate cleavages defines the proteases acting on them.  We are developing proteomics based methodologies, including selective protein labeling, multi-dimensional electrophoresis, and mass spectrometry techniques, to identify the products of proteolysis in vivo.