Molecular morphology of the tetrodotoxin-binding sodium channel protein from Electrophorus electricus in solubilized and reconstituted preparations.
The appearance of detergent-solubilized voltage-regulated sodium channel protein was recently characterized by this laboratory. Negative-staining revealed rod-shaped particles measuring 40 X 170 A. Further studies have suggested that the actual configuration of this protein may be quite different from the rod-shaped structures. Freeze-fracture and freeze-etch images of the protein in reconstituted membranes indicated that the channel is cylindrical with a diameter of 100 A and a minimum length of 80 A. Experiments with two detergent systems (Lubrol-PX and sodium cholate) enabled us to explain the discrepancy between this structure and the rod-shaped particles visualized earlier. Negative staining in either detergent at low pH (4.5) produced rod-shaped structures. As the pH was increased, doughnut-shaped particles, consistent with the structure of the protein in freeze-etch, appeared in negative stain. The tendency of the protein to change shape under different pH conditions appears to be a peculiar property of this protein.
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D004557:Electric Organ / Q000378:metabolism; D004593:Electrophorus; D005614:Freeze Fracturing; D006651:Histocytochemistry; D007473:Ion Channels / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels; D012995:Solubility; D013779:Tetrodotoxin / Q000378:metabolism*
D002352:Carrier Proteins; D007473:Ion Channels; D015222:Sodium Channels; C023790:tetrodotoxin-binding protein; D013779:Tetrodotoxin; D012964:Sodium