| Research Abstract |
Clostridium botulinum neurotoxins (Mr.150kDa) associate with nontoxic components in the cultures or in the foods, and become large complexes designated 12S (300 kDa), 16S (500 kDa), and 19S (900 kDa) progenitor toxins. Type A strain produces three formes of toxins, 12S,16S,and 19S,and type B,C,and D produce two formes of toxins, 12S and16S.Types E,F and G produce only one type of toxin ; types E and F produce 12S toxin, and type G produces 16 toxin. The 12S toxin consists of a neurotoxin and a nontoxic component showing no hemagglutinin (HA) activity, described here as a NTNH.The 16S and 19S toxins are formed by conjugation of 12S toxin with HA.The structure of progenitor toxins was clarified by both genetic- and protein chemical- analyzes. The conclusions drawn are 1) any types of HAs consist of four subcomponents, 53,33,22-23, and 17 kDa, which associated in the ratio of 1 : 2 : 1 : 1,2) the 22-2 kDa subcomponent consists of several proteins having a slightly different Mr, 3) type A
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19S and 16S toxins consist of the same protein components. It was postulated that the 19S toxin is a dimmer of the 16S toxin cross-linked by HA-33,4) the NTNHs of type A,C,and D 12S toxins have a cleavage on their N-terminal regions, and are separated into two parts on SDS-PAGE.A multiple alignment of N-terminal regions of the NTNHs of types A,C,D,E,and F demonstrated that the cleavage occurs in a region including a short repeat sequence, and that types E and F which produce only 12S toxin lack this region. It was thought that the processing in NTNH is the reason why the 12S and 16S (and 19S) toxins exist in the same culture, 5) the receptors of red blood cells for HA arre different depending on the types of toxins ; A and B toxins bind to neutral lipids, whereas C and D toxins bind to sialic acids in both glicolipids (such as GM3 and sialylparagloboside) and glycoproteins (such as glycophorin), 6) In type C,HA-33 and HA-53 out of four subcomponents of HA,have the binding activity to the erythrocytes, 7) HA plays an important role for the progenitor toxin to bind to the epithelial cells of small intestine, that leads to efficient absorption of the HA-positive toxins is small intestine s compared with the HA-negative toxin. Less
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