Analysis of the multi-pore system of alamethicin in a lipid membrane

Abstract

The electrical properties of an alamethicin multi-pore system have been studied by voltage-jump current-relaxation experiments (this paper) and by autocorrelation and spectral analysis (following paper). With these methods a slow time constant and a fast time constant were observed which differ by about one to three orders of magnitude depending on the experimental conditions. Steady-state current and time constants were analyzed as functions of voltage, alamethicin concentration and temperature. Within experimental error the data obtained with these different methods are in good agreement. The experimentally measured relation between the voltage and alamethicin concentration dependence of the slow relaxation time fits into a model of an alamethicin pore which adopts consecutive pore states and which decays only from the lowest state. It indicates that the uptake of one alamethicin molecule by the existing pore and, in formal equivalence, the transfer of about one positive elementary charge across the membrane are associated with the transition from a given pore conductance state to the next higher state. From the voltage and alamethicin concentration dependence of the pore formation rate evidence shows that a hexameric preaggregate exists at the membrane interface out of which two to three molecules are simultaneously inserted into the membrane to form the pore nucleus. The effects of different voltage pretreatment on the experimentally determined parameters have been investigated and are discussed in detail.Alamethicin has been shown by Mueller and Rudin (1968), Baumann and Mueller (1974) and Mueller (1976a, b) to be a model substance which induces excitability phenomena in artificial lipid membranes. A way to elucidate the underlying molecular mechanism of alamethicin action has been opened through single channel investigations by Gordon and Haydon (1972)

Alamethicin Supramolecular Organization in Lipid Membranes from 19F Solid-State NMR

“…As many as 20 distinguishable conductance states have been described (12). The fluctuations between the stepwise K þ and Cl À conductivities are consistent with the various sizes of the transmembrane channels due to the presence of different oligomeric states of the helix bundles (13,14) (reviewed in (1,2)). It has been suggested that these pore structures may consist of at least three (15), four (1), or even five subunits (16).…”

“…Magic-angle spinning (MAS) solid-state NMR techniques utilizing dipolar recoupling have been developed to measure distances between 13 C-isotopically labeled peptides, and the global structure can be reconstructed from the resulting data. However, most of these techniques yield only relatively short intermolecular distances (up to~5 Å ).…”

Autocatalytic transport of the peptide antibiotics suzukacillin and alamethicin across lipid membranes

“…Under the influence of an electrical potential certain aggregates form membrane sprig chmels which are in a fast exchange with the monomer pool. Conclusive evidence for this mechanism was recently presented by Boheim and Kolb [2]. Jn most of these investigations both sides of the membrane contained equal amounts of peptide antibiotic.…”

“…This discovery prompted elaborate studies in many laboratories, which resulted in a detailed concept for the ionophoric action of alamethicin and several analogues ( [2] covers the literature comprehensively). It was shown that alamethicin adsorbs to the membrane surface where monomers coexist with aggregates.…”

Structural fluctuations between two conformational states of a transmembrane helical peptide are related to its channel‐forming properties in planar lipid membranes

“…It was reported several years ago (Menestrina et al, 1986) that even completely hydrophobic polypeptides of the type Boc-(AlaAib-Ala-Aib-Ala-),-OMe (Boc, t-butoxycarbonyl; Aib, aaminoisobutyric acid), which can adopt a straight transmembrane helical structure, induce voltage-dependent ionic conductance across planar lipid bilayers, but it was not possible in this particular case to observe the low-conductance states observed with the structurally related peptide antibiotic alamethicin (Boheim and Kolb, 1978;Hanke and Boheim, 1980). How can one change the sequence of these simple peptides in order to realize stable membrane channels?…”