But how is EF-Tu modified, they wondered? And does it help P. aeruginosa establish an infection? This study answers those questions.
Using a host of techniques, including mass spectrometry, site directed mutagenesis of key residues in the protein, and genetic loss of function/gain of function studies, they found that P. aeruginosa only makes small changes to EF-Tu to get it to mimic this powerful ligand. P. aeruginosa transfers three methyl groups to a lysine on EF-Tu, giving it a structure similar to ChoP and allowing it to fit in the PAFR receptor in the way ChoP does.
But the modified EF-Tu not only looks like ChoP, in many ways it works like ChoP: testing in cultures of human airway cells shows that the modification of EF-Tu enables the bacterium to adhere to human cells.
"It allows [P. aeruginosa] to adhere to the cells and invade," says Goldberg. "And it seems to be involved in virulence in mouse models. It might also impact persistence in the lung."
As an environmental pathogen, P. aeruginosa lives in soil, water, and other environments outside the body, a fact that may offer a clue why it uses this re-purposed protein as a virulence factor. Proteins that can be put to work in both worlds - in the environment and the in the human host - would be useful to P. aeruginosa in much the way a spork can allow you to enjoy both the coleslaw and the pudding in your take out dinner.
"Its interaction with humans is accidental. It's an
|Contact: Jim Sliwa|
American Society for Microbiology