M. Tomizawa et al., Photoaffinity labeling of insect nicotinic acetylcholine receptors with a novel [H-3]azidoneonicotinoid, J NEUROCHEM, 78(6), 2001, pp. 1359-1366
The nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel
in the insect CNS and a target for major insecticides. Here we use photoaff
inity labeling to approach the functional architecture of insect nAChRs. Tw
o candidate 5-azido-6-chloropyridin-3-yl photoaffinity probes are evaluated
for their receptor potencies: azidoneonicotinoid (AzNN) with an acyclic ni
troguanidine moiety; azidodehydrothiacloprid. Compared to their non-azido p
arents, both probes are of decreased potencies at Drosophila (fruit fly) an
d Musca (housefly) receptors but AzNN retains full potency at the Myzus (ap
hid) receptor. [H-3]AzNN was therefore radio-synthesized at high specific a
ctivity (84 Ci/mmol) as a novel photoaffinity probe. [H-3]AzNN binds to a s
ingle high-affinity site in Myzus that is competitively inhibited by imidac
loprid and nicotine and further characterized as to its pharmacological pro
file with various nicotinic ligands. [H-3]AzNN photoaffinity labeling of My
zus and Homalodisca (leafhopper) detects a single radiolabeled peak in each
case displaceable with imidacloprid and nicotine and with molecular masses
corresponding to similar to 45 and similar to 56 kDa, respectively. The ph
otoaffinity-labeled receptor in both Drosophila and Musca has imidacloprid-
and nicotine-sensitive profiles and migrates at similar to 66 kDa. These p
hotoaffinity-labeled polypeptides are considered to be the insecticide-bind
ing subunits of native insect nAChRs.