Diphtheria toxin A (DTA)

Diphtheria toxin A (DTA) is the catalytic domain (fragment A) of diphtheria toxin, a potent exotoxin secreted primarily by *Corynebacterium diphtheriae*. DTA is responsible for the toxin's enzymatic activity, functioning as a mono-ADP-ribosyltransferase: it transfers ADP-ribose from cellular NAD+ to diphthamide on eukaryotic elongation factor 2 (eEF-2), thereby inhibiting protein synthesis and rapidly inducing cell death[1][2][3][6]. DTA consists of the amino-terminal 24 kDa region of the full diphtheria toxin protein and operates after delivery into the cytosol, which is mediated by fragment B (receptor-binding and transmembrane domains)[3][4]. Although DTA itself is not a naturally occurring independent polypeptide, it has been extensively used in engineered fusion proteins (immunotoxins), exploiting its ability to kill target cells selectively when directed by specific binding domains[3]. This has made it a valuable research and therapeutic tool, albeit with significant safety concerns due to its high cytotoxicity and immunogenicity. Note: The name "diphtheria toxin A" or "fragment A" refers specifically to the catalytic (enzyme) domain of the complete diphtheria toxin protein, not to a full-length receptor or endogenous human target.

Other names

Fragment A of diphtheria toxinDTADiphtheria toxin catalytic domainDT-A

ADP-ribosylation of eukaryotic elongation factor 2 (eEF-2), thereby halting protein synthesis; Cell death via inhibition of translation.