PhD candidate Rob Fieldhouse
As the number of antibiotic-resistant bacteria continues to grow, researchers in the Department of Molecular and Cellular Biology are developing new ways to fight these pathogens. Disease-causing bacteria have long plagued humanity, and their ability to pass on antibiotic-resistant genes means that researchers need to stay one step ahead.
“Bacterial pathogens use a variety of different methods to affect the host or the target,” says Rob Fieldhouse, a PhD candidate supervised by Prof. Rod Merrill. Protein toxins are one of the weapons in the bacterial arsenal. Cholera, diphtheria and pertussis toxins modify intracellular proteins, which kills the cell. Some toxins affect signalling molecules, while others affect the cell’s cytoskeleton.
“One of the overall goals of the lab is to combat antibiotic resistance using small molecules,” says Fieldhouse. “Instead of trying to kill the whole organism, one strategy is to disarm it. You take away the weaponry without actually killing the pathogen.” This approach is complementary to more traditional vaccination strategies in which inactivated toxins help the body recognize and attack the real toxins.
A self-described “toxin hunter,” Fieldhouse uses a tactic called fold recognition to find and identify new toxins by comparing new sequences to toxin structures that have already been characterized. “Knowing the structure of the toxin will help you design inhibitors for the toxin,” he says. “If you can figure out that structural problem, then you can start to work on the second problem, which is to come up with a small molecule that will bind the toxin and inactivate it.”
The researchers use X-ray crystallography to identify structural characteristics by aiming X-rays at toxin crystals, which produce patterns that yield key structural information. The lab team, which includes technician Dawn White and postdoctoral fellow Amanda Rochon, also tests the toxins in yeast to see if the cells live or die.
Most recently, the lab is studying the disease-causing mechanisms of Certhrax, an anthrax-like toxin produced by Bacillus cereus, and Chelt, a toxin produced by Vibrio cholerae. The researchers believe Certhrax enters the target cell like other toxins, but kills in another way, while Chelt has a different way of getting in. “We think it kills in a very traditional way, but we think it has a new entry mechanism,” says Fieldhouse.
This research is funded by the Natural Sciences and Engineering Research Council, the Canadian Institutes of Health Research and the Human Frontier Science Program.