Justyne Ogdahl, NIH Trainee 2020-2021
Graduate Program: Molecular and Cellular Biology
Lab: Peter Chien
Research Interests: Understand the mechanism by which bacterial and mitochondrial Lon’s dynamic conformation cycle engages with substrates, small molecules and DNA in order to regulate degradation
In all domains of life, regulated protein degradation is essential to maintain protein homeostasis. Because proteolysis is irreversible, this process is highly regulated. In bacteria, energy dependent AAA+ proteases degrade most of the unwanted proteins from the cell. My work will focus specifically on the Lon protease which is found in both bacterial cells and in the mitochondria. Lon is primarily known as a quality control protease degrades misfolded proteins by recognizing exposed hydrophobic regions normally buried in folded proteins. This contrasts with other AAA+ proteases like ClpXP which recognize specific substrates in a highly discriminate fashion. In the Chien lab, we study regulated proteolysis using the model organism, Caulobacter crescentus, a gram-negative alpha-proteobacterium. Using Caulobacter, we have uncovered principles of how proteins are degraded, why they are degraded, and what happens if proteolysis is misregulated.
According to the endosymbiotic theory of eukaryotic evolution, mitochondria decent from ancestral alpha-proteobacteria. Previous studies performed in our lab have established mechanistic similarity between Caulobacter Lon and that found in mitochondria. Specifically, we found that DNA and other ligands can allosterically regulate Caulobacter Lon and that this function is preserved in mitochondria and virulent bacteria. For mitochondria, the ability of Lon to bind DNA is important for protection against genotoxic stress (as it is in Caulobacter). For the human pathogen Vibrio cholera, we have found that binding to cyclic nucleotides regulates Lon in a manner critical for virulence.
My PhD work aims to focus on the mechanism by which bacterial and mitochondrial Lon engages with substrates, small molecules and DNA in order to regulate degradation. We have found that DNA and small molecule binding can be stimulatory or inhibitory and isolated specific sites on the Lon protease are critical for this regulation. Recent structural data has shown that Lon can adopt an open or closed conformation depending on substrate binding, suggesting a dynamic conformation cycle that we propose is regulated also by DNA/small molecules. My work will focus on how these Lon conformational states are allosterically regulated in both bacteria and mitochondria systems. It is clear that mitochondria dysfunction underlie many human proteinopathies, such as Alzheimer’s disease (AD) and cancers. Virulent bacteria also rely on Lon to enable their host infection. Therefore, my work will have far reaching applied impact across a range of important areas.