Molecular Structure of Clostridium Botulinum Progenitor Toxins

Abstract

Progenitor toxin and its components Clostridium botulinum "progenitor toxin" is defined as the ancestral toxin appearing first in foods and culture. 2 It is now known that the progenitor toxin is a complex of a toxic and a nontoxic component (Fig. 1). The molecule of the progenitor toxin dissociates when exposed to pH 7.2 or higher. The dissociated toxic component was named "derivative toxin.,,2 The derivative toxin is the true "neurotoxin," but it does not seem entitled to be called "botulinum toxin," because it is highly toxic only when administered parenterally; ingestion of derivative toxin would not cause botulism. "Botulism" is the term used to designate a neuroparalytic disease such as that caused by oral ingestion of sausages containing the toxin. Molecular structure of progenitor toxins The molecular structure of the progenitor toxin is not uniform (Fig. 2). Until now, three forms have been distinguished based on the molecular size. They are "M toxin," "L toxin" and "LL toxin." M stands for "medium-sized," L for "large-sized," and LL for "extra-large sized." The molecular weight of M toxin is approximately 300 kDa with an S20 w of 12; that of L toxin approximately 500 kDa with an S20 w of 16; that of LL toxin approximately 900 kDa with an S20,w of 1'9. 7 Progenitor toxin (botulinum toxin) Toxic component Nontoxic component A Toxic component Neurotoxin S toxin D Nontoxic component Fig. 1. Molecular structure of C. botulinum progenitor toxins.