Effect of the state of association of melittin and phospholipids on their reciprocal binding.

In solutions of increasing ionic strength, the molecular weight of melittin varies from 2840 (monomeric melittin) to 11200. This polymerization, concomitant with an important change in conformation (Talbot, J.C., Dufourcq, J., De Bony, J., Faucon, J.F. and Lussan, C. (1979) FEBS Lett. 102, 191-193), is accompanied by a significant alteration in the partial specific volume of the molecule. The binding of melittin to phospholipids (phosphatidylserine, lysolecithin, dihexanoyl-, dioctanoyl- and lysolauroylphosphatidylcholine) depends on the state of association of the toxin and on the critical micelle concentration of lipids. No interaction is observed between monomeric melittin and free lipids, whereas tetrameric melittin can bind free lipids to form mixed micelles. At phospholipid concentrations above the critical micelle concentration, melittin in any state of self-association can bind lipids. The mixed micelles formed at saturation appear to be independent of the initial state of association of melittin.