Membrane-modifying properties of the pore-forming peptaibols saturnisporin SA IV and harzianin HA V.

Harzianin HA V and saturnisporin SA IV are alpha-amino isobutyric-containing peptides with 18- and 20-residue chain length, respectively. They were isolated from in vitro cultures of Trichoderma species and their sequences were determined by the combined use of positive ion FAB mass spectrometry and NMR. In organic solvent solution, both peptides exhibited the same predominant alpha-helical secondary structure including a hinge at the level of the central Pro residue, as deduced from NMR data. Their interaction with neutral phospholipid bilayers was shown to induce leakage of the material entrapped in small unilamellar vesicles composed of egg phosphatidylcholine/cholesterol (7/3). When incorporated into neutral planar lipid bilayers, they promoted voltage-gated channels. The concentration- and voltage-dependences of the ionic conductances induced by these peptides were studied in macroscopic current-voltage experiments. Single-channel measurements showed that whilst SA IV developed non-integral multi-open states similar to those induced by alamethicins, but with faster kinetics, the shorter analogue, HA V promoted much smaller-sized conducting aggregates in agreement with macroscopic conductance data.