EFFECT OF SDS AND THE ZWITTERIONIC SURFACTANT HPS ON THE CONFORMATION AND HEMOLYTIC ACTIVITY OF St I AND St II, TWO ISOTOXINS FROM Stichodactyla helianthus

Lanio, M.E.(1), Alvarez, C.(1), Pazos, F.(1), Martinez, D.(1), Martínez, Y.(1), Casallanovo, F.(2), Campos, A.M.(3), Abuin, E.(3), Schreier,S.(2), Lissi, E.(3)

(1)University of Havana, Cuba, (2)University of São Paulo, Brazil, (3)University of Santiago, Chile.

Pore forming toxins are extremely sensitive to changes in their conformation. We have shown  that  the  hemolytic  activity of Sticholysins I and II  (St I  and St II) is dependent of those factors that change their conformation. There are no data regarding the effect of detergents on the structural and functional characteristics of cytolysins. In the present work, the interaction of St I and St II with sodium dodecyl sulfate (SDS) and N-hexadecyl-N-N'-dimethyl-3-ammonio-1-propane-sulfonate (HPS) was characterized. At low surfactant concentrations SDS leads to the formation of aggregates and the proteins show an increase in intrinsic fluorescence intensity and reduced quenching by acrylamide, with an almost total loss of their hemolytic activity. At higher surfactant concentrations it was observed a loss of the protein-aggregated state. This produces a decrease in fluorescence intensity, increase in quenching efficiency by acrylamide, loss of the native tertiary conformation, and increase in a-helix content. However, the toxins partially recover their hemolytic activity. The results suggest that, as a consequence of the interaction with SDS micelles, the proteins adopt an a-helix-enriched, more open structure. This structure might be able to leave the micelle and convert to the native b-structure-rich conformation in the presence of red blood cell membranes, recovering the ability to form the pore. On the other hand, the binding constants of St I and St II faced to HPS were ca.0.5 - 0,7mM^-1. The changes elicited by HPS lead to a more expanded tertiary conformation than the native structure. In spite of this, the toxins fully retain their hemolytic activities. This indicates that spectroscopic changes can be poor predictors of toxin activity.

CORRESPONDENCE TO:

María Eliana Lanio, Centro de Estudio de Proteínas, Facultad de Biología, Universidad de la Habana, Calle 25, entre J e I, Vedado, Ciudad Habana, Cuba, Email: mlanio@infomed.sld.cu