Michael Johnson
| Student: Michael Johnson |
 |
| Undergraduate Institution: | Duke University |
| Email: | Michael_johnson@med.unc.edu |
| Department: | Biochemistry & Biophysics |
| PI: | Matthew Redinbo |
| Research Summary: | Pseudomonas aeruginosa is a motile bacteria involved in more than 10% of all nosocomial infections. This opportunistic pathogen is highly prevalent in patients who suffer from cystic fibrosis, burns, or are otherwise immunocompromised. P. aeruginosa relies on type IV piIi (T4P) to establish and maintain infections by attaching to the host. T4P functions as an oscillatory motor involving pilus extension and retraction which leads to a type of motility known as twitching. Regulation of this motor in P. aeruginosa, however, has remained a mystery. PilY1, a T4P protein, has been found to be necessary for functional pilus biogenesis. The crystal structure of C-terminal PilY1 (614-1163) revealed a conserved calcium-binding site required for bacterial translocation. This site is also conserved in other T4P containing pathogens with PilY1 homologues such as Neisseria gonorrhea PilC. We show that preventing calcium binding by PilY1 via a calcium chelator or point mutation disrupts P. aeruginosa twitching motility by eliminating surface pili. In contrast, placing a lysine in this loop to mimic the charge of a bound calcium is also detrimental to motility by producing an abundance of non-functional surface pili. Our data indicate that calcium binding and release by the calcium loop identified in the crystal structure controls the opposing forces of pilus extension and retraction respectively. Thus, PilY1 is an essential, calcium-dependent regulator of bacterial twitching motility. |
