DPH1 Gene Mutations Identify a Candidate SAM Pocket in Radical Enzyme Dph1•Dph2 for Diphthamide Synthesis on EF2

Bacterial exotoxins in medicine: potential value and perspectives

Bacterial exotoxins are protein- or peptide-based substances secreted by bacteria with high toxicity and specificity. They have diverse mechanisms of action on host cells, leading to host injury by destroying the cellular structure or interfering with physiological functions. With the continuous progress in biotechnology, bacterial exotoxins have broad application prospects in immunotherapy, vaccine development, drug design, and other fields. Appropriate modification of exotoxins can lead to the preparation of highly efficient immune agents and targeted drugs, which brings new hope for overcoming difficult diseases. This study provides a comprehensive and in-depth introduction to the application of bacterial exotoxins in the field of medicine and further explores the potential value of bacterial exotoxins, which is expected to make greater contributions to human health in the future.

Diphthamide formation in Arabidopsis requires DPH1-interacting DPH2 for light and oxidative stress resistance

Diphthamide is a posttranslationally modified histidine residue of eukaryotic TRANSLATION ELONGATION FACTOR 2 (eEF2) and the target of diphtheria toxin in human cells. In yeast and mammals, the 4Fe-4S cluster-containing proteins Dph1 and Dph2 catalyze the first biosynthetic step of diphthamide formation. Here, we identify Arabidopsis (Arabidopsis thaliana) DPH2 and show that it is required for diphthamide biosynthesis, localizes to the cytosol, and interacts physically with AtDPH1. Arabidopsis dph2 mutants form shorter primary roots and smaller rosettes than the wild type, similar to dph1 mutants which we characterized previously. Additionally, increased ribosomal -1 frameshifting error rates and attenuated TARGET OF RAPAMYCIN (TOR) kinase activity in dph2 mutants also phenocopy the dph1 mutant. Beyond the known heavy metal hypersensitivity and heat shock tolerance of dph1, we show here that both dph1 and dph2 mutants are hypersensitive to elevated light intensities and oxidative stress and that wild-type Arabidopsis seedlings accumulate diphthamide-unmodified eEF2 under oxidative stress. Both mutants share the deregulation of 1,186 transcripts associated with several environmental and hormone responses. AtDPH1 and AtDPH2 do not complement the corresponding mutants of Saccharomyces cerevisiae. In summary, DPH2 and DPH1 interact to function inter-dependently in diphthamide formation, the maintenance of translational fidelity, wild-type growth rates, and TOR kinase activation, and they contribute to mitigating damage from elevated light intensities and oxidative stress. Under oxidative stress, a dose-dependent loss of diphthamide could potentiate downstream effects in a feed-forward loop. This work advances our understanding of translation and its interactions with growth regulation and stress responses in plants.

Diphthamide - a conserved modification of eEF2 with clinical relevance

Diphthamide, a complex modification on eukaryotic translation elongation factor 2 (eEF2), assures reading-frame fidelity during translation. Diphthamide and enzymes for its synthesis are conserved in eukaryotes and archaea. Originally identified as target for diphtheria toxin (DT) in humans, its clinical relevance now proves to be broader than the link to pathogenic bacteria. Diphthamide synthesis enzymes (DPH1 and DPH3) are associated with cancer, and DPH gene mutations can cause diphthamide deficiency syndrome (DDS). Finally, new analyses provide evidence that diphthamide may restrict propagation of viruses including SARS-CoV-2 and HIV-1, and that DPH enzymes are targeted by viruses for degradation to overcome this restriction. This review describes how diphthamide is synthesized and functions in translation, and covers its clinical relevance in human development, cancer, and infectious diseases.