Structure and function of the voltage sensor of sodium channels probed by a beta-scorpion toxin.
Abstract
Voltage sensing by voltage-gated sodium channels determines the electrical excitability of cells, but the molecular mechanism is unknown. beta-Scorpion toxins bind specifically to neurotoxin receptor site 4 and induce a negative shift in the voltage dependence of activation through a voltage sensor-trapping mechanism. Kinetic analysis showed that beta-scorpion toxin binds to the resting state, and subsequently the bound toxin traps the voltage sensor in the activated state in a voltage-dependent but concentration-independent manner. The rate of voltage sensor trapping can be fit by a two-step model, in which the first step is voltage-dependent and correlates with the outward gating movement of the IIS4 segment, whereas the second step is voltage-independent and results in shifted voltage dependence of activation of the channel. Mutations of Glu(779) in extracellular loop IIS1-S2 and both Glu(837) and Leu(840) in extracellular loop IIS3-S4 reduce the binding affinity of beta-scorpion toxin. Mutations of positively charged and hydrophobic amino acid residues in the IIS4 segment do not affect beta-scorpion toxin binding but alter voltage dependence of activation and enhance beta-scorpion toxin action. Structural modeling with the Rosetta algorithm yielded a three-dimensional model of the toxin-receptor complex with the IIS4 voltage sensor at the extracellular surface. Our results provide mechanistic and structural insight into the voltage sensor-trapping mode of scorpion toxin action, define the position of the voltage sensor in the resting state of the sodium channel, and favor voltage-sensing models in which the S4 segment spans the membrane in both resting and activated states.
Fichier principal
Cestele_6Sep05_JBC_1_.pdf (6.02 Mo)
Télécharger le fichier
Cestele_Fig._9.tif (6.94 Mo)
Télécharger le fichier
Cestele_Fig_1.eps (78.31 Ko)
Télécharger le fichier
Cestele_Fig_2.eps (117.63 Ko)
Télécharger le fichier
Cestele_Fig_3.EPS (111.53 Ko)
Télécharger le fichier
Cestele_Fig_4.eps (97.81 Ko)
Télécharger le fichier
Cestele_Fig_5.eps (172.63 Ko)
Télécharger le fichier
Cestele_Fig_6.eps (156.25 Ko)
Télécharger le fichier
Cestele_Fig_7.eps (169.44 Ko)
Télécharger le fichier
Cestele_Fig_8.eps (76.66 Ko)
Télécharger le fichier
Origin : Files produced by the author(s)
Format : Other
Format : Other
Format : Other
Format : Other
Format : Other
Format : Other
Format : Other
Format : Other
Format : Other
Loading...