We identified Tf2, the first β-scorpion toxin from the venom of the Brazilian scorpion Tityus fasciolatus. Tf2 is identical to Tb2-II found in Tityus bahiensis. We found that Tf2 selectively activates human (h)Nav1.3, a neuronal voltage-gated sodium (Nav) subtype implicated in epilepsy and nociception. Tf2 shifts hNav1.3 activation voltage to more negative values, thereby opening the channel at resting membrane potentials. Seven other tested mammalian Nav channels (Nav1.1-1.2; Nav1.4-1.8) expressed in Xenopus oocytes are insensitive upon application of 1 μM Tf2. Therefore, the identification of Tf2 represents a unique addition to the repertoire of animal toxins that can be used to investigate Nav channel function.
Acknowledgments: Parts of the research in this publication were supported by the National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health (NIH) under award number R00NS073797 (F.B.) and by CNPq (564.223/2010-7)/FAPDF (193.000.471/2011) (INOVATOXIN project) (E.F.S). T.S.C. is a graduate student financed by CNPq and CAPES Foundation. S.C.R. and C.B.F.M. are graduate students supported by CNPq. E.F.S. receives support from CNPq, and FAPDF.