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Biophysical Journal 85:971-981 (2003)
© 2003 The Biophysical Society

Interaction of Viscotoxins A3 and B with Membrane Model Systems: Implications to Their Mechanism of Action

Marcela Giudici * {dagger}, Roberto Pascual *, Laura de la Canal {dagger}, Karola Pfüller {ddagger}, Uwe Pfüller {ddagger} and José Villalaín *

* Instituto de Biología Molecular y Celular, Universidad "Miguel Hernández", Campus de Elche, E-03202 Elche-Alicante, Spain; {dagger} Instituto de Investigaciones Biológicas, Universidad Nacional de Mar del Plata, AR-7600 Mar del Plata, Argentina; and {ddagger} Institut für Phytochemie, Private Universität Witten/Herdecke gGmbH, D-58453 Witten, Germany

Correspondence: Address reprint requests to Dr. José Villalaín, Instituto de Biología Molecular y Celular, Universidad "Miguel Hernández", E-03202 Elche-Alicante, Spain. Tel.: +34-966-658-759; Fax: +34-966-658-758; E-mail: jvillalain{at}umh.es.

Viscotoxins are small proteins that are thought to interact with biomembranes, displaying different toxic activities against a varied number of cell types, being viscotoxin A3 (VtA3) the most cytotoxic whereas viscotoxin B (VtB) is the less potent. By using infrared and fluorescence spectroscopies, we have studied the interaction of VtA3 and VtB, both wild and reduced ones, with model membranes containing negatively charged phospholipids. Both VtA3 and VtB present a high conformational stability, and a similar conformation both in solution and when bound to membranes. In solution, the infrared spectra of the reduced proteins show an increase in bandwidth compared to the nonreduced ones indicating a greater flexibility. VtA3 and VtB bind with high affinity to membranes containing negatively charged phospholipids and are motional restricted, their binding being dependent on phospholipid composition. Whereas nonreduced proteins maintain their structure when bound to membranes, reduced ones aggregate. Furthermore, leakage experiments show that wild proteins were capable of disrupting membranes whereas reduced proteins were not. The effect of VtA3 and VtB on membranes having different phospholipid composition is diverse, affecting the cooperativity and fluidity of the membranes. Viscotoxins interact with membranes in a complex way, most likely organizing themselves at the surface inducing the appearance of defects that lead to the destabilization and disruption of the membrane bilayer.




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