Increase of permeability of synaptosomes and liposomes by the heavy chain of tetanus toxin
Högy, B.; Dauzenroth, M.E.; Hudel, M.; Weller, U.; Habermann, E.
Toxicon Official Journal of the International Society on Toxinology 30(1): 63-76
In search of a role for the heavy chain of tetanus toxin in poisoning, its actions on natural and artificial membranes have been assessed. The heavy chain increases the permeability of synaptosomes to lactate dehydrogenase and potassium ions, and promotes the outward shift of the lipophilic cation tetraphenylphosphonium which is a particularly sensitive indicator for depolarization. Independent of the assay system the potency is decreased by the addition of the light chain and by treatment of the synaptosomes with the C-terminal fragment C of the heavy chain, but not with its N-terminal fragment .beta.2. Single- or two-chain toxin itself is inactive, and so are the light chain or the two heavy chain fragments .beta.2 and C. Lipsomes were made from phosphatidylcholine and phosphatidylserine or gangliosides and loaded with calcein. At pH 6 the outflow of calcein is promoted in the order heavy chain > toxin .mchgt. fragment .beta.2, and the action of toxin is promoted by ganglioside. At pH 5, fragment .beta.2 is nearly as active as the heavy chain and more potent than the toxin. The heavy chain, but neither of the fragments, strongly adsorbed in hydrophobic interaction chromatography and caused aggregation of polystyrene-divinylbenzene beads. Evidence for polymerization of heavy chains is lacking in zonal centrifugation. It is concluded that both domains of the heavy chain co-operate to exert the membranal events described, and that the heavy chain is partially hidden by the light chain in the complete toxin molecule.