A novel tarantula toxin stabilizes the deactivated voltage sensor of bacterial sodium channel.

Voltage-gated sodium channels (NaV s) are activated by transiting the voltage sensor from the deactivated to the activated state. The crystal structures of several bacterial NaV s 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 NaV s. We screened fractions from several venoms and characterized a cystine knot toxin called JZTx-27 from the venom of tarantula Chilobrachys jingzhao as a high-affinity antagonist of the prokaryotic NaV s NsV Ba (nonselective voltage-gated Bacillus alcalophilus ) and NaChBac (bacterial sodium channel from Bacillus halodurans ) (IC50 = 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 NsV Ba, whereas the local anesthetic drug lidocaine was shown to antagonize NsV Ba without affecting channel gating. Mutation analysis confirmed that JZTx-27 bound to S3-4 linker of NsV Ba, with F98 being the critical residue in determining toxin affinity. All electrophysiological data and in silico analysis suggested that JZTx-27 trapped VSM of NsV Ba in one of the deactivated states. In mammalian NaV s, JZTx-27 preferably inhibited the inactivation of NaV 1.5 by targeting the fourth transmembrane domain. To our knowledge, this is the first report of peptide antagonist for prokaryotic NaV s. More important, we proposed that JZTx-27 stabilized the NsV Ba VSM in the deactivated state and may be used as a probe to determine the structure of the deactivated VSM of NaV s.-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.