E. coli toxin YjjJ (HipH) is a Ser/Thr protein kinase that impacts cell division, carbon metabolism and ribosome assembly

Protein Ser/Thr kinases are post-translational regulators of key molecular processes in bacteria, such as cell division and antibiotic tolerance. Here we characterize the E. coli toxin YjjJ (HipH), a putative protein kinase annotated as a member of the family of HipA-like Ser/Thr kinases which are involved in antibiotic tolerance. Using SILAC-based phosphoproteomics we provide experimental evidence that YjjJ is a Ser/Thr protein kinase and its primary protein substrates are the ribosomal protein RpmE (L31) and the carbon storage regulator CsrA. YjjJ activity impacts ribosome assembly, cell division and central carbon metabolism but it does not increase antibiotic tolerance as does its homologue HipA. Intriguingly, overproduction of YjjJ and its kinase-deficient variant can activate HipA and other kinases, pointing to a crosstalk between Ser/Thr kinases in E. coli.