D-ALPHA-3, A NEW FUNCTIONAL ALPHA-SUBUNIT OF NICOTINIC ACETYLCHOLINE-RECEPTORS FROM DROSOPHILA

Nicotinic acetylcholine (ACh) receptors (nAChRs) are important excitat ory neurotransmitter receptors in the insect CNS, We have isolated and characterized the gene and the cDNA of a new nAChR subunit from Droso phila. The predicted mature nAChR protein consists of 773 amino acid r esidues and has the structural features of an ACh-binding alpha subuni t. It was therefore named D alpha 3, for Drosophila alpha-subunit 3. T he d alpha 3 gene maps to the X chromosome at position 7E. The propert ies of the D alpha 3 protein were assessed by expression in Xenopus oo cytes. D alpha 3 did not form functional receptors on its own or in co mbination with any Drosophila beta-type nAChR subunit. Nondesensitizin g ACh-evoked inward currents were observed when Da3 was coexpressed wi th the chick beta 2 subunit. Half-maximal responses were at similar to 0.15 mu M ACh with a Hill coefficient of similar to 1.5. The snake ve nom component alpha-bungarotoxin (100 nM) efficiently but reversibly b locked D alpha 3/beta 2 receptors, suggesting that D alpha 3 may be a component of one of the previously described two classes of toxin bind ing sites in the Drosophila CNS.