Voltage-gated sodium channels (Nas) are activated by transiting the voltage sensor from the deactivated to the activated state. The crystal structures of several bacterial Nas have captured the voltage sensor module (VSM) in an activated state， but structure of the deactivated voltage sensor remains elusive. In this study， we sought to identify peptide toxins stabilizing the deactivated VSM of bacterial Nas. We screened fractions from several venoms and characterized a cystine knot toxin called JZTx-27 from the venom of tarantula as a high-affinity antagonist of the prokaryotic Nas NsBa (nonselective voltage-gated ) and NaChBac (bacterial sodium channel from ) (IC = 112 nM and 30 nM， respectively). JZTx-... More
Voltage-gated sodium channels (Nas) are activated by transiting the voltage sensor from the deactivated to the activated state. The crystal structures of several bacterial Nas have captured the voltage sensor module (VSM) in an activated state， but structure of the deactivated voltage sensor remains elusive. In this study， we sought to identify peptide toxins stabilizing the deactivated VSM of bacterial Nas. We screened fractions from several venoms and characterized a cystine knot toxin called JZTx-27 from the venom of tarantula as a high-affinity antagonist of the prokaryotic Nas NsBa (nonselective voltage-gated ) and NaChBac (bacterial sodium channel from ) (IC = 112 nM and 30 nM， respectively). JZTx-27 was more efficacious at weaker depolarizing voltages and significantly slowed the activation but accelerated the deactivation of NsBa， whereas the local anesthetic drug lidocaine was shown to antagonize NsBa without affecting channel gating. Mutation analysis confirmed that JZTx-27 bound to S3-4 linker of NsBa， with F98 being the critical residue in determining toxin affinity. All electrophysiological data and analysis suggested that JZTx-27 trapped VSM of NsBa in one of the deactivated states. In mammalian Nas， JZTx-27 preferably inhibited the inactivation of Na1.5 by targeting the fourth transmembrane domain. To our knowledge， this is the first report of peptide antagonist for prokaryotic Nas. More important， we proposed that JZTx-27 stabilized the NsBa VSM in the deactivated state and may be used as a probe to determine the structure of the deactivated VSM of Nas.-Tang， C.， Zhou， X.， Nguyen， P. T.， Zhang， Y.， Hu， Z.， Zhang， C.， Yarov-Yarovoy， V.， DeCaen， P. G.， Liang， S.， Liu， Z. A novel tarantula toxin stabilizes the deactivated voltage sensor of bacterial sodium channel.
