Transcriptional and post-translational regulation by the Ser/Thr protein kinase HipH

Dynamic protein phosphorylation is one of the cornerstones in bacterial signal transduction. In recent years the eukaryotic type Ser/Thr kinase HipA received increasing attention due to its role in conferring antibiotic tolerance. In Escherichia coli HipA is encoded together with HipB on the hipBA operon, forming a toxin antitoxin (TA) module. If not neutralized by its antitoxin HipB, HipA phosphorylates different substrate pools in E. coli, promoting growth stop and inducing persistence. Phylogenetic analysis revealed that homologues of hipBA like TA systems are widespread among various bacterial species, including clinically relevant strains [1]. The roles of these different TA modules are still debated and include genetic chromosome stabilization, phage defense and antibiotic tolerance. In a recent study we investigated the monocistronic hipA homologue HipH (yjjJ), demonstrating its toxic effect on cell division and identified several novel phosphorylation targets [2]. Intriguingly, HipH carries a putative DNA binding helix-turn-helix (HTH) domain at its N-terminus which is usually found in HipB-like antitoxins to regulate expression of its own TA module.

In this work we investigate the role of the HTH domain of HipH regarding its ability to bind DNA/RNA and its potential role in transcriptional regulation. We show that the HTH-domain of HipH, in contrast to HipB, is not involved in regulating its own expression but is instead essential for the toxicity of HipH. Thereby, we show via shotgun proteomics that the HTH-domain regulates a variety of different genes, including potential virulence factors. We therefore postulate, that this domain provides a regulatory function on the transcriptional level for HipH in addition to the post-translational regulation by its kinase activity.

Gerdes K, Bærentsen R, Brodersen DE. Phylogeny Reveals Novel HipA-Homologous Kinase Families and Toxin-Antitoxin Gene Organizations. mBio. 2021 Jun 29;12(3):e0105821.

Gratani FL, Englert T, Nashier P, Sass P, Czech L, Neumann N, Doello S, Mann P, Blobelt R, Alberti S, Forchhammer K, Bange G, Höfer K, Macek B. E. coli Toxin YjjJ (HipH) Is a Ser/Thr Protein Kinase That Impacts Cell Division, Carbon Metabolism, and Ribosome Assembly. mSystems. 2023