Flammutoxin, a cytolysin from the edible mushroom Flammulina velutipes, forms two different types of voltage-gated channels in lipid bilayer membranes.
Flammutoxin, a 31-kDa cardiotoxic and cytolytic protein from the edible mushroom Flammulina velutipes, has been shown to assemble into a pore-forming annular oligomer with outer and inner diameters of 10 and 5 nm on the target cells [Tomita et al., Biochem. J. 333 (1998) 129-137]. Here we studied electrophysiological properties of flammutoxin channels using planar lipid bilayer technique, and found that flammutoxin formed two types of moderately cation-selective, voltage-gated channels with smaller and larger current amplitudes (1-4.5 pA and 20-30 pA, respectively, at 20 mV) in the lipid bilayers composed of phospholipid and cholesterol. The larger-conductance single channel showed the properties of a wide water-filled pore such as a linear relationship between channel conductance and salt concentration of the bathing solution. The functional diameter of the larger-conductance channel was estimated to be 4-5 nm by measuring the current conductance in the presence of polyethylene glycols of various sizes. In contrast, the smaller-conductance single channels showed a non-linear current to voltage curve and a saturating conductance to increasing salt concentration. These results suggest that the larger-conductance channel of flammutoxin corresponds to the hemolytic pore complex, while the smaller-conductance channel may reflect the intermediate state(s) of the assembling toxin.
Tadjibaeva
G
G
Department of Molecular and Cellular Biology, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan.
Sabirov
R
R
Tomita
T
T
D000363:Agaricales; D000818:Animals; D005656:Fungal Proteins / Q000633:toxicity*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry* / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D008564:Membrane Potentials; D008567:Membranes, Artificial; D009183:Mycotoxins / Q000633:toxicity*; D012492:Salts
D005656:Fungal Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D009183:Mycotoxins; D012492:Salts; C011823:FTX protein, Flammulina velutipes