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Conductance studies on trichotoxin_A50E and implications for channel structure
H Duclohier1, G M Alder, C L Bashford
1Interactions Cellulaires et Moléculaires, UMR 6026 Centre National de la Recherche Scientifique-Université de Rennes I, 35042 Rennes Cedex, France. herve-duclohier@wanadoo.fr
Biophysical Journal
|September 4, 2004
Summary
Trichotoxin A50E forms hexameric channels in lipid bilayers, preferentially transporting cations. Its channel structure, informed by crystal data, differs from alamethicin, showing a single conductance state per experiment.
Area of Science:
- Biophysics
- Structural Biology
- Membrane Biophysics
Background:
- Trichotoxin A50E is an 18-residue peptaibol with a recently determined crystal structure.
- Peptaibols form ion channels in lipid bilayers, but their precise structures and conductances are not fully understood.
Purpose of the Study:
- To investigate the conductance properties of Trichotoxin A50E in neutral planar lipid bilayers.
- To elucidate the oligomeric state and ion transport characteristics of Trichotoxin A50E channels.
- To develop a structural model for the Trichotoxin A50E channel based on experimental data and crystal structure.
Main Methods:
- Macroscopic current-voltage (I-V) measurements in planar lipid bilayers.
- Conductance measurements under various ion gradients.
- Analysis of single-channel conductance states.
- Construction of a hexameric channel model based on crystal structure and conductance data.
Main Results:
- Trichotoxin A50E channels exhibit moderate voltage-sensitivity.
- Channel formation is primarily hexameric, with cation selectivity observed.
- Single experiments show one conductance state, but multiple levels exist across experiments.
- A tightly-packed hexameric model is compatible with observed conductance and molecular dimensions.
Conclusions:
- Trichotoxin A50E forms stable hexameric channels with cation preference.
- The channel structure is distinct from alamethicin, reflecting differences in helical conformation.
- The proposed hexameric model provides a framework for understanding Trichotoxin A50E channel function.