Diphthamide

Diphthamide is a post-translationally modified histidine amino acid found in archaeal and eukaryotic elongation factor 2 (eEF-2).
Structure.
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.
Biological function.
Diphthamide ensures translation fidelity.
The presence or absence of diphthamide is known to affect NF-κB or death receptor pathways.
Biosynthesis.
Diphthamide is biosynthesized from histidine and "S"-adenosyl methionine.