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Diphteria toxin induces fusion of small unilamellar vesicles at low ph

par Cabiaux, Véronique ;Vandenbranden, Michel ;Ruysschaert, Jean Marie ;Falmagne, Paul
Référence Archives of physiology and biochemistry, 92, 2, page (BP4)
Publication Publié, 1984

Article révisé par les pairs

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Résumé :

Diphteria toxin (DT) consists of a single 62 000 daltons polypeptide chain. The N-terminal segment (fragment A) inhibits protein synthesis in most mammalian cells by catalytically inactivating elongation factor 2. To interact with elongation factor 2, fragment A must cross a membrane barrier and enter the cytoplasm. In this report, we present evidence that DT is able to induce, at low pH, the fusion of small unilamellar lipid vesicles which results probably from a strong destabilization of the lipid bilayer. Fluorescence depolarization and differential scanning calorimetry make it possible to demonstrate the mixing of the lipid phases. Mixing of the internal aqueous compartments of liposomes was established using the terbium fluorescence technique. From our results, it can be assumed that DT-mediated fusion process is not total or that leakage of the fluorescent markers occurs during the initial step of the fusion. This hypothesis seems probable since DT is known as a potent pore formator (Donovan et al., 1981). This phenomenon should however be transient. Melittin also induces fusion of unilamellar phospholipid vesicles (Morgan et al., 1983). Melittin contains 2 αhelixes linked by a proline residue; one of them is amphipathic and is supposed to insert into the lipid membrane (Tosteson & Tosteson, 1981). The predicted secondary structure of DT fragment B revealed a region made of 2 αhelixes linked by a proline residue (Lambotte et al., 1980). Again, one of the helix is amphipathic with a large apolar surface. Furthermore, this helical segment has been predicted to be a transverse lipid associating domain and could be made responsible for pore formation in conductance measurements (Deleers et al., 1983). At the present time, we cannot give any explanation for the relationships between the structure and the fusogenic properties of the two toxins. © 1984 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.