Diphthamide

Abstract: Diphthamide, a posttranslational modification of translation elongation factor 2 that is conserved in all eukaryotes and archaebacteria and is the target of diphtheria toxin, is formed in yeast by the actions of five proteins, Dph1 to -5, and a still unidentified amidating enzyme. Dph2 and Dph5 were previously identified. Here, we report the identification of the remaining three yeast proteins (Dph1, -3, and -4) and show that all five Dph proteins have either functional (Dph1, -2, -3, and -5) or sequence (Dph4) homologs in mammals. We propose a unified nomenclature for these proteins (e.g., HsDph1 to -5 for the human proteins) and their genes based on the yeast nomenclature. We show that Dph1 and Dph2 are homologous in sequence but functionally independent. The human tumor suppressor gene OVCA1, previously identified as homologous to yeast DPH2, is shown to actually be HsDPH1. We show that HsDPH3 is the previously described human diphtheria toxin and Pseudomonas exotoxin A sensitivity required gene 1 and that DPH4 encodes a CSL zinc finger-containing DnaJ-like protein. Other features of these genes are also discussed. The physiological function of diphthamide and the basis of its ubiquity remain a mystery, but evidence is presented that Dph1 to -3 function in vivo as a protein complex in multiple cellular processes.

Abstract: The bacteria causing diphtheria, whooping cough, cholera and other diseases secrete mono-ADP-ribosylating toxins that modify intracellular proteins. Here, we describe four structures of a catalytically active complex between a fragment of Pseudomonas aeruginosa exotoxin A (ETA) and its protein substrate, translation elongation factor 2 (eEF2). The target residue in eEF2, diphthamide (a modified histidine), spans across a cleft and faces the two phosphates and a ribose of the non-hydrolysable NAD+ analogue, βTAD. This suggests that the diphthamide is involved in triggering NAD+ cleavage and interacting with the proposed oxacarbenium intermediate during the nucleophilic substitution reaction, explaining the requirement of diphthamide for ADP ribosylation. Diphtheria toxin may recognize eEF2 in a manner similar to ETA. Notably, the toxin-bound βTAD phosphates mimic the phosphate backbone of two nucleotides in a conformational switch of 18S rRNA, thereby achieving universal recognition of eEF2 by ETA. The bacterial toxins that make diphtheria, whooping cough and cholera so dangerous are all mono-ADP-ribosylating toxins. A high-resolution crystal structure of one of these toxins in a complex with its substrate translation elongation factor 2 (EF2), has now been obtained. The toxin is shown to mimic normal interactions between EF2 and the 80S ribosome, ensuring universal recognition of the translation factor and making it almost impossible for hosts to develop resistance. The structure also has implications for the mechanism of translocation on the 80S ribosome.

Abstract: Complementary DNA clones, pHEW1 and pRE2, coding for hamster and rat polypeptide chain elongation factor 2 (EF-2), respectively, were isolated and sequenced. It was shown that the cDNA insert in pHEW1 contains a 2574-base-pair open reading frame coding for an 857-amino acid polypeptide with Mr 95,192, excluding the initiation methionine. Comparative studies of sequence homology among EF-2 and several GTP-binding proteins show that five regions in the amino-terminal position of EF-2, corresponding to about 160 amino acids, show homology with GTP-binding proteins, including protein synthesis elongation and initiation factors, mammalian ras proteins, and transducin. The carboxyl-terminal half of EF-2 contains several regions that have 34-75% homology with bacterial elongation factor G. These results suggest that the amino-terminal region of EF-2 participates in the GTP-binding and GTPase activity whereas the carboxyl-terminal region interacts with ribosomes. Finally, the sequence provides direct evidence that diphthamide (2-[3-carboxy-amido-3-(trimethylammonio)propyl]histidine), the site of ADP-ribosylation by diphtheria toxin, is produced by post-translational modification of a histidine residue in the primary translational product.

Abstract: Molecular structure activity studies for some Diphthamide Nano particles derivatives indicate that the conformational characteristics along with the nature and position of the substituents on the Diphthamide Nano particles derivatives ring play an important role in their biological and biochemical activities (Figure 1) [1-7]. Therefore, we have calculated the optimized molecular geometries of some Diphthamide Nano particles derivatives. Calculations are carried out on the structures of these medical, medicinal and pharmaceutical Nano drugs using Hartree–Fock calculations and also Density Functional Theory (DFT) by performing HF, PM3, MM2, MM3, AM1, MP2, MP3, MP4, CCSD, CCSD(T), LDA, BVWN, BLYP and B3LYP levels of theory using the standard 31G, 6–31G*, 6–31+G*, 6–31G(3df, 3pd), 6–311G, 6–311G* and 6–311+G* basis sets of the Gaussian 09. The comparative heats of formation and Natural Bond Orbital (NBO) charges are calculated for these Diphthamide Nano particles derivatives. We have finally obtained some conformational rules in terms of the natures and positions of the substituents on the Diphthamide Nano particles derivatives ring.