Clostridium botulinum group III strains are able to produce cytotoxins, C2 toxin and C3 exotoxin,
along with botulinum neurotoxin types C and D. C2 toxin and C3 exotoxin produced by this organism
are the most important members of bacterial ADP-ribosyltransferase superfamily. Both toxins
have distinct pathophysiological functions in the avian and mammalian hosts. The members of this superfamily
transfer an ADP-ribose moiety of NAD+ to specific eukaryotic target proteins. The present
review describes the structure, function and evolution aspects of these toxins with a special emphasis to
the development of veterinary vaccines. C2 toxin is a binary toxin that consists of a catalytic subunit
(C2I) and a translocation subunit (C2II). C2I component is structurally and functionally similar to the
VIP2 and iota A toxin whereas C2II component shows a significant homology with the protective antigen
from anthrax toxin and iota B. Unlike C2 toxin, C3 toxin is devoid of translocation/binding subunit.
Extensive studies on their sequence-structure-function link spawn additional efforts to understand the
catalytic mechanisms and target recognition. Structural and functional relationships with them are often
determined by using evolutionary constraints as valuable biological measures. Enzyme-deficient mutants
derived from these toxins have been used as drug/protein delivery systems in eukaryotic cells.
Thus, current knowledge on their molecular diversity is a well-known perspective to design immunotoxin
or subunit vaccine for C. botulinum infection.
Keywords: Veterinary vaccines, subunit vaccine clostridium botulinum, molecular evolution, immunotoxin, molecular pathogenesis.
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