Ion-channel properties of mastoparan, a 14-residue peptide from wasp venom, and of MP3, a 12-residue analogue

Mastoparan, a 14-residue peptide, has been investigated with respect to its ability to form ion channels in planar lipid bilayers. In the presence of 0.3 - 3.0 μ M mastoparan, two types of activity are seen. Type I activity is characterized by discrete channel openings, exhibiting multiple con­ductance levels in the range 15-700 pS. Type II activity is characterized by transient increases in bilayer conductance, up to a maximum of about 650 pS. Both type I and type II activities are voltage dependent. Channel activation occurs if the compartment containing mastoparan is held at a positive potential; channel inactivation if the same compartment is held at a negative potential. Channel formation is dependent on ionic strength; channel openings are only observed at KCl concentrations of 0.3 M or above. Furthermore, raising the concentration of KCl to 3.0 M stabilizes the open form of the channel. Mastoparan channels are weakly cation selective, P K/Cl ≈ 2. A 12-residue analogue, des -Ile 1 , Asn 2 mastoparan, preferentially forms type I channels. The ion channels formed by these short peptides may be modelled in terms of bundles of transmembrane α -helices.