Domain 2 of Drosophila Para Voltage-Gated Sodium Channel Confers Insect Properties to a Rat Brain Channel (original) (raw)

2002, The Journal of Neuroscience

The ability of the excitatory anti-insect-selective scorpion toxin AahIT (Androctonus australis hector) to exclusively bind to and modify the insect voltage-gated sodium channel (NaCh) makes it a unique tool to unravel the structural differences between mammalian and insect channels, a prerequisite in the design of selective pesticides. To localize the insect NaCh domain that binds AahIT, we constructed a chimeric channel composed of rat brain NaCh ␣-subunit (rBIIA) in which domain-2 (D2) was replaced by that of Drosophila Para (paralytic temperaturesensitive). The choice of D2 was dictated by the similarity between AahIT and scorpion ␤-toxins pertaining to both their binding and action and the essential role of D2 in the ␤-toxins binding site on mammalian channels. Expression of the chimera rBIIA-ParaD2 in Xenopus oocytes gave rise to voltage-gated and TTX-sensitive NaChs that, like rBIIA, were sensitive to scorpion ␣-toxins and regulated by the auxiliary subunit ␤ 1 but not by the insect TipE. Notably, like Drosophila Para/TipE, but unlike rBIIA/␤ 1 , the chimera gained sensitivity to AahIT, indicating that the phyletic selectivity of AahIT is conferred by the insect NaCh D2. Furthermore, the chimera acquired additional insect channel properties; its activation was shifted to more positive potentials, and the effect of ␣-toxins was potentiated. Our results highlight the key role of D2 in the selective recognition of anti-insect excitatory toxins and in the modulation of NaCh gating. We also provide a methodological approach to the study of ion channels that are difficult to express in model expression systems.