Arginine-rhamnosylation as new strategy to activate translation elongation factor P
The ribosomal protein synthesis is dependent on auxiliary proteins such as the universal elongation factor P (EF-P). After unravelling its long-concealed function—alleviating ribosome stalling upon encountering a polyproline stretch—Prof. Lassak recruited me for this project prior to my PhD to investigate bacterial EF-Ps featuring an arginine at a critical position where other organisms harbour various post-translationally modified amino acids. With arginine modifications being extremely rare in nature, this project developed into an exciting quest to unravel a mechanism occurring in a subset of species comprising various human pathogens. A bioinformatics analysis brought our attention to a gene of unknown function that consistently co-occurred with arginine EF-Ps. Making use of an in vivo reporter system based on a polyproline-containing transcriptional activator, we then could show that the gene codes for a glycosyl transferase that is functionally linked to EF-P in general, and the arginine in particular. Prompted by the results of a mass spectrometric analysis, we performed in vivo experiments with knockout strains to eventually identify rhamnose as the post-translational arginine modification. Notably, this work also comprised my first protein engineering experiments, resulting in a follow-up publication (Volkwein et al. Front. Microbiol. 2019 10:1148).