Trimethylation of Elongation Factor-Tu by the Dual Thermoregulated Methyltransferase EftM Does Not Impact Its Canonical Function in Translation.

The Pseudomonas aeruginosa methyltransferase EftM trimethylates elongation factor-Tu (EF-Tu) on lysine 5 to form a post-translational modification important for initial bacterial adherence to host epithelial cells. EftM methyltransferase activity is directly temperature regulated. The protein stability of EftM is tuned with a melting temperature (T) around 37 °C such that the enzyme is stable and active at 25 °C, but is completely inactivated by protein unfolding at higher temperatures. This leads to higher observable levels of EF-Tu trimethylation at the lower temperature. Here we report an additional layer of thermoregulation resulting in lower eftM mRNA transcript level at 37 °C compared to 25 °C and show that this regulation occurs at the level of transcription initiation. To begin to define the impact of this system on P. aeruginosa physiology, we demonstrate that EF-Tu is the only observable substrate for EftM. Further, we interrogated the proteome of three different wild-type P. aeruginosa strains, their eftM mutants, and these mutants complemented with eftM and conclude that trimethylation of EF-Tu by EftM does not impact EF-Tu's canonical function in translation. In addition to furthering our knowledge of this Pseudomonas virulence factor, this study provides an intriguing example of a protein with multiple layers of thermoregulation.