Identification of an intra-molecular disulfide bond in the sodium channel beta 1-subunit

The sodium channel ?1 subunit is non-covalently associated with the pore-forming ?-subunits, and has been proposed to act as a modulator of channel activity, regulator of channel cell surface expression and cell adhesion molecule. Its importance is evident since mutations of the ?1 subunit cause neurologic and cardiovascular disorders. The first described ?1 subunit mutation is the C121W, that is related to generalized epilepsy with febrile seizures plus (GEFS+), a childhood genetic epilepsy syndrome. This mutation changed a conserved cysteine residue in position 121 into a tryptophan, putatively disrupting a disulfide bridge that should normally maintain the ?1 extracellular immunoglobulin-like fold. Using the 2-D-diagonal-SDS-PAGE technique, we demonstrated the existence of this putative disulfide bridge in the Ig-like extracellular domain of the ?1 subunit and its disruption in the epileptogenic C121W mutant.