Paddling Along the Voltage Gated Sodium Channel Galaxy with Sea Anemone Toxins: Structural Studies of the Interaction between the Paddle Motif from Nav1.5DIV and Sea Anemone Toxin

Voltage gated sodium channels (VGSC) are membrane proteins that serve an important function in the central nervous system (CNS), peripheral nervous system (PNS), and cardiac muscles amongst others. The main function of VGSC is in the propagation of electrical signals by depolarizing excitable cells. Nine mammalian VGSC subtypes have been characterized, NaV1.1 – NaV1.9, that are expressed in a tissue specific manner, each with unique gating properties. Numerous diseases have been linked to defects in VGSC including epilepsy, mental retardation, long QT syndrome, and Brugada disease. Furthermore, these channels are one of the primary targets of toxins from venomous animals. Animal toxins have been used as an excellent probe to study the function of VGSC due to their specific and potent effect on VGSC. By solving the structural details of the interaction between animal toxins and VGSC we will gain more insight into the function of these channels and contribute to rational drug development against these channels. We determined the structures of NaV1.5 DIV S3b-S4a (also known as the paddle motif) from the cardiac sodium channel as well as that of a sea anemone toxin Anthopleurin A (ApA) known to bind that region of the channel by Nuclear Magnetic Resonance (NMR) spectroscopy in dodecylphosphocholine (DPC) micelles. In addition, we determined what residues on the toxin interact with the micelle (and, by extension, the membrane). We further determined important interactions between the toxin and the paddle motif and used this data to build a HADDOCK model of the complex between NaV1.5 DIV S3b-S4a and ApA toxin