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The biosynthesis and biological function of diphthamide.

ABSTRACT: Eukaryotic and archaeal elongation factor 2 contains a unique post-translationally modified histidine residue, named diphthamide. Genetic and biochemical studies have revealed that diphthamide biosynthesis involves a multi-step pathway that is evolutionally conserved among lower and higher eukaryotes. During certain bacterial infections, diphthamide is specifically recognized by bacterial toxins, including diphtheria toxin, Pseudomonas exotoxin A and cholix toxin. Although the pathological relevance is well studied, the physiological function of diphthamide is still poorly understood. Recently, many new interesting developments in understanding the biosynthesis have been reported. Here, we review the current understanding of the biosynthesis and biological function of diphthamide.

SUBMITTER: Su X

PROVIDER: S-EPMC4280834 | biostudies-literature | 2013 Nov-Dec

REPOSITORIES: biostudies-literature

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The biosynthesis and biological function of diphthamide.

Su Xiaoyang X Lin Zhewang Z Lin Hening H

Critical reviews in biochemistry and molecular biology 20130823 6

Eukaryotic and archaeal elongation factor 2 contains a unique post-translationally modified histidine residue, named diphthamide. Genetic and biochemical studies have revealed that diphthamide biosynthesis involves a multi-step pathway that is evolutionally conserved among lower and higher eukaryotes. During certain bacterial infections, diphthamide is specifically recognized by bacterial toxins, including diphtheria toxin, Pseudomonas exotoxin A and cholix toxin. Although the pathological relev ...[more]

PMID: 23971743

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Project description:A mutant of Saccharomyces cerevisiae defective in the S-adenosylmethionine (AdoMet)-dependent methyltransferase step of diphthamide biosynthesis was selected by intracellular expression of the F2 fragment of diphtheria toxin (DT) and shown to belong to complementation group DPH5. The DPH5 gene was cloned, sequenced, and found to encode a 300-residue protein with sequence similarity to bacterial AdoMet:uroporphyrinogen III methyltransferases, enzymes involved in cobalamin (vitamin B12) biosynthesis. Both DPH5 and AdoMet:uroporphyrinogen III methyltransferases lack sequence motifs commonly found in other methyltransferases and may represent a new family of AdoMet:methyltransferases. The DPH5 protein was produced in Escherichia coli and shown to be active in methylation of elongation factor 2 partially purified from the dph5 mutant. A null mutation of the chromosomal DPH5 gene did not affect cell viability, in agreement with other studies indicating that diphthamide is not required for cell survival. The dph5 null mutant survived expression of three enzymically attenuated DT fragments but was killed by expression of fully active DT fragment A. Consistent with these results, elongation factor 2 from the dph5 null mutant was found to have weak ADP-ribosyl acceptor activity, which was detectable only in the presence of high concentrations of fragment A.

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Project description:Diphthamide is a modified histidine residue which is uniquely present in archaeal and eukaryotic elongation factor 2 (EF-2), an essential GTPase responsible for catalyzing the coordinated translocation of tRNA and mRNA through the ribosome. In part due to the role of diphthamide in maintaining translational fidelity, it was previously assumed that diphthamide biosynthesis genes (dph) are conserved across all eukaryotes and archaea. Here, comparative analysis of new and existing genomes reveals that some archaea (i.e., members of the Asgard superphylum, Geoarchaea, and Korarchaeota) and eukaryotes (i.e., parabasalids) lack dph. In addition, while EF-2 was thought to exist as a single copy in archaea, many of these dph-lacking archaeal genomes encode a second EF-2 paralog missing key residues required for diphthamide modification and for normal translocase function, perhaps suggesting functional divergence linked to loss of diphthamide biosynthesis. Interestingly, some Heimdallarchaeota previously suggested to be most closely related to the eukaryotic ancestor maintain dph genes and a single gene encoding canonical EF-2. Our findings reveal that the ability to produce diphthamide, once thought to be a universal feature in archaea and eukaryotes, has been lost multiple times during evolution, and suggest that anticipated compensatory mechanisms evolved independently.

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