Research

Bacterial pathogens are a serious threat to human health, particularly as our most important weapons against them, antibiotics, are losing their effectiveness due to the spread of resistant organisms. There is an urgent need to increase our understanding of bacterial cell functions, so that we can better understand our enemy, and identify weak points for potential therapeutic attack. Our laboratory is especially interested in the envelope that surrounds all bacterial cells. This cell envelope is a made up of multiple layers, including phospholipid membranes and a rigid cell wall made of the polymer peptidoglycan. The cell envelope protects bacteria from damaging molecules and conditions in their environment. Furthermore, virulence factors are assembled in the cell envelope, or must pass through it on their way out of the bacterial cell. Maintaining the integrity and functions of the cell envelope is critical at all times, including when bacteria infect a human host where they are exposed to harsh conditions, immune system attack, and must deploy their virulence factors in order to survive. We combine genetics, molecular biology and biochemistry, along with various infection models, to study important functions in the cell envelope of the human pathogen Pseudomonas aeruginosa. P. aeruginosa is a frequent cause of serious opportunistic human infections, especially in hospitalized patients and people suffering from Cystic Fibrosis.

The CtpA protease

We discovered that the carboxyl-terminal processing protease CtpA is essential for P. aeruginosa virulence because it impacts systems associated with pathogenesis, including the type III secretion system (T3SS). Our experiments have shown that CtpA works in complex with the outer membrane lipoprotein LbcA to control potentially dangerous cell wall hydrolases by degrading them. We are exploring how CtpA activity is controlled, the role of its substrates, and how they affect virulence and cell-envelope functions. As part of this work we also collaborate with Huilin Li's laboratory at the Van Andel Institute for structure-function analysis of CtpA, LbcA and their substrates.

Expanding interests in the P. aeruginosa cell envelope

Our interests have also begun to move into understanding the role of a second carboxyl-terminal processing protease that is present in P. aeruginosa, which is an apparent ortholog of the well-characterized E. coli protease Prc. Overall, our goal is to achieve a global understanding of how carboxyl-terminal processing proteases contribute to cell envelope functions, protein export systems, and virulence. Carboxyl-terminal processing proteases are widespread in bacteria, and many of them have been linked to virulence and other significant phenotypes. Therefore, this work will provide insight that is relevant to many important organisms.

Finally, we are beginning to characterize some novel P. aeruginosa envelope proteins discovered in genetic screens, some of which are widely conserved but completely uncharacterized. These proteins appear to impact fundamental processes occurring in the cell envelope, including the control of cell wall remodeling.

All of our research offers the promise to contribute to our understanding of how bacteria control critical functions in their cell envelopes, and especially the metabolism of one of the most important components, and a major target for many antibiotics, their cell wall.