In the opportunistic pathogen, Pseudomonas aeruginosa, we have found that the normally cytoplasmic translation initiation factor, elongation factor-Tu (EF-Tu), is surface exposed and modified as detected with antibodies to phosphorylcholine (PC). This modification is more prominent on P. aeruginosa strains grown at 25?C compared to 37?C. In Preliminary Studies, we tested strains with mutations in genes known to be involved in choline synthesis, metabolism, or transport and found no effect on PC expression, compared to the wild-type strain. We then screened the entire comprehensive P. aeruginosa strain PA14 transposon mutant library and have found a single gene that is responsible for the post-translational modification of EF-Tu. Compared to the wild-type strain, a strain deleted for this gene, referred to as eftM, adheres less well to airway epithelial cells and colonizes less well in a mouse model of acute pneumonia. Through a combination of approaches, including mass spectrometry of purified modified or unmodified EF-Tu, site-directed mutagenesis of key residues, and genetic loss of function/gain of function studies, we demonstrate that P. aeruginosa mimics platelet-activating factor (PAF) by the presence of three methyl groups on lysine 5 of EF-Tu resulting in a chemical structure similar to PC. However how this post-translational modification affects the export and/or normal function of EF-Tu is not known. This may represent a novel mechanism of control for this abundant bacterial protein and may be implicated in the regulation of bacterial protein synthesis. We will take a multipronged approach to address how EF-Tu is exported and how this modification affects protein synthesis. We will localize where in the cell this modification occurs and which regions of EF-Tu are surface exposed and PC modified, using subcellular fractionation, electron microscopy, and mass spectrometry. We will further determine how modified EF-Tu affects protein synthesis. The knowledge and the tools generated from these studies will provide insights into this novel post-translational modification, inhibition of which may define new targets for interrupting bacterial-host interactions and thus the pathogenesis of P. aeruginosa.
This project will increase our fundamental understanding of protein synthesis in the opportunistic pathogen, Pseudomonas aeruginosa. By the completion of this study we will have assembled critical information about export of the abundant normally cytoplasmic EF-Tu and the role of a unique post-translational modification of this protein that we have detected in P. aeruginosa. Since we have found the modified EF-Tu is important for adherence to host cells, defining how to interrupt the export and/or modification of EF-Tu may provide novel targets for therapeutic interventions.