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. Virulence factors are also 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 and especially when bacteria infect a human host and 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 to study important functions in the cell envelope of Pseudomonas aeruginosa - a frequent cause of serious opportunistic human infections, especially in hospitalized patients and people suffering from Cystic Fibrosis.

C-terminal processing proteases

Bacterial carboxyl-terminal processing proteases (CTPs) are widely conserved enzymes that play key roles in vital cellular processes. They are also directly linked to the virulence of some pathogens. Despite their importance, the roles of most CTPs are poorly characterized. P. aeruginosa has two CTPs: Prc and CtpA. CtpA is crucial for function of the type 3 secretion system and acute virulence. Prc is required for mucoid conversion in some isolates from people with cystic fibrosis. We are studying the roles, mechanisms and impacts of these CTPs. Together, they target proteins involved in virulence, antibiotic resistance, gene regulation, and other unknown functions. One common theme is that many bacterial CTPs is to degrade proteins that affect the cell wall, with implications for virulence and antibiotic resistance.

Autolysin control mechanisms

Almost all bacterial cells are encased by a peptidoglycan cell wall. They must make new peptidoglycan to grow and divide, but they must also coordinate this with cell wall lysis to incorporate the new material into the existing meshwork. The enzymes that cleave the cell wall, collectively known as autolysins, must be controlled to avoid catastrophe if they cleave at the wrong time or in the wrong place. Understanding how bacteria achieve this control could provide new foundational knowledge needed to ultimately help design disrupting interventions. At least four of the CtpA substrates are autolysins, which makes CtpA one major autolysin control mechanism we have discovered in P. aeruginosa - but it is not the only one. We have also found a novel inhibitor/anti-inhibitor system that controls the activity of the lytic transglycosylase MltF. These findings are motivating us to search for more autolysin control mechanisms, wit the potential for fundamental biological advances in autolysin regulation of relevance in many bacterial species.