Dα3, a New Functional α Subunit of Nicotinic Acetylcholine Receptors from Drosophila

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Abstract
Nicotinic acetylcholine (ACh) receptors (nAChRs) are important excitatory neurotransmitter receptors in the insect CNS. We have isolated and characterized the gene and the cDNA of a new nAChR subunit from Drosophila. The predicted mature nAChR protein consists of 773 amino acid residues and has the structural features of an ACh‐binding α subunit. It was therefore named Dα3, for Drosophilaα‐subunit 3. The dα3 gene maps to the X chromosome at position 7E. The properties of the Dα3 protein were assessed by expression in Xenopus oocytes. Dα3 did not form functional receptors on its own or in combination with any Drosophilaβ‐type nAChR subunit. Nondesensitizing ACh‐evoked inward currents were observed when Dα3 was coexpressed with the chick β2 subunit. Half‐maximal responses were at ∼0.15 µM ACh with a Hill coefficient of ∼1.5. The snake venom component α‐bungarotoxin (100 nM) efficiently but reversibly blocked Dα3/β2 receptors, suggesting that Dα3 may be a component of one of the previously described two classes of toxin binding sites in the Drosophila CNS.

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