This week we profile a recent publication in Structure from the laboratory of Dr. Lisa Craig at Simon Fraser University.
Can you provide a brief overview of your lab’s current research focus?
We are investigating the structure, function and assembly of Type IV pili, hairlike filaments found on the surfaces of many bacterial pathogens. Type IV pili are long thin polymers made up of thousands of copies of a protein subunit called the “major pilin”. They also have several low abundance “minor pilins” that are critical for pilus assembly and functions but their functions are poorly understood. Type IV pili are both adhesive and retractile, which means that they assemble, bind to surfaces or to pili on adjacent bacteria, or to DNA or bacteriophage, then retract, pulling the bacteria along surfaces or into tight aggregates with other bacteria, or pull DNA or bacteriophage into their periplasm. As such, they are critical for pathogenesis. Some Type IV pili are also able to secrete substances like toxins and enzymes across the outer membrane of the bacteria and into its surroundings. We are using x-ray crystallography, cryo-electron microscopy, genetics and microbiology to understand the structure of Type IV pili at the atomic level, the mechanisms by which they are assembled and retracted, and the role that the minor pilins play in these processes.
What is the significance of the findings in this publication?
In this paper we present the structures of Type IV pili from two bacterial pathogens of major medical importance, Pseudomonas aeruginosa and Neisseria gonorrhoeae. P. aeruginosa use Type IV pili to adhere to the lungs of cystic fibrosis patients, causing deadly infections, and N. gonorrhoeae use their Type IV pili to adhere to and invade cells of the urogenital tract to cause the sexually transmitted disease gonorrhea. These Type IV pili are several microns in length and extremely thin, less than 1/100th of a micron in diameter, yet they have remarkable tensile strength, flexibility and elasticity. Our structures reveal the interactions between the pilin subunits within these pili that drive pilus assembly and impart upon them their extraordinary biophysical properties.
What are your next steps for this research?
We wish to understand the molecular events that lead to pilus assembly, retraction and secretion. The diarrheal pathogen Vibrio cholerae possesses one of the simplest Type IV pilus systems known. In this system the major pilin is the building block for these pili, but the minor pilin appears to control the switches from pilus assembly to retraction to secretion. We are working to understand how the minor pilin performs these functions. We are also testing Type IV pili as delivery systems for antibiotics. Our strategy is to attach antibiotics to carrier proteins that bind specifically to the tips of Type IV pili for delivery into the bacterium upon pilus retraction. This approach would allow us to precisely target a given pathogen, avoiding non-specific killing of other beneficial bacteria that are often collateral damage in antibiotic treatment regimes, and it would deliver antibiotics across the bacterial outer membrane and into the cell, overcoming a major barrier for many existing drugs that are too large to cross this membrane in a passive manner.
This research was funded by:
The work described in this paper is a result of an international collaboration between researchers at Simon Fraser University, the University of Virginia in the US, and Institut Necker-Enfants Malades in Paris, France. Funding was provided by the Canadian Institutes for Health Research (CIHR), the US National Institutes of Health (NIH) and the Agence Nationale de la Recherche of France.
