Diphthamide
Diphthamide is a post-translationally modified histidine amino acid found in archaeal and eukaryotic elongation factor 2 (eEF-2).
Dipthamide is named after the toxin produced by the bacterium Corynebacterium diphtheriae, which targets diphthamide.[1] Besides this toxin, it is also targeted by exotoxin A from Pseudomonas aeruginosa.[1][2] It is the only target of these toxins.[2]
Structure and biosynthesis
Diphthamide is proposed to be a 2-[3-carboxyamido-3-(trimethylammonio)propyl]histidine. Though this structure has been confirmed by X-ray crystallography, its stereochemistry is uncertain.[1][3]
Diphthamide is biosynthesized from histidine and S-adenosyl methionine (SAM).[1] The side chain bound to imidazole group and all methyl groups come from SAM. The whole synthesis takes place in three steps:[1]
- transfer of 3-amino-3-carboxypropyl group from SAM
- transfer of three methyl groups from SAM – synthesis of diphtine
- amidation – synthesis of diphthamide
In eukaryotes, this biosynthetic pathway contains a total of 7 genes (Dph1-7).[1]
Biological function
Diphthamide ensures translation fidelity.[1]
The presence or absence of diphthamide is known to affect NF-κB or death receptor pathways.[4]
References
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