Atypical nicotinic agonist bound conformations conferring subtype selectivity.
The nicotinic acetylcholine (ACh) receptor (nAChR) plays a crucial role in excitatory neurotransmission and is an important target for drugs and insecticides. Diverse nAChR subtypes with various subunit combinations confer differential selectivity for nicotinic drugs. We investigated the subtype selectivity of nAChR agonists by comparing two ACh-binding proteins (AChBPs) as structural surrogates with distinct pharmacological profiles [i.e., Lymnaea stagnalis (Ls) AChBP of low neonicotinoid and high nicotinoid sensitivities and Aplysia californica (Ac) AChBP of high neonicotinoid sensitivity] mimicking vertebrate and insect nAChR subtypes, respectively. The structural basis of subtype selectivity was examined here by photoaffinity labeling. Two azidoneonicotinoid probes in the Ls-AChBP surprisingly modified two distinct and distant subunit interface sites: loop F Y164 of the complementary or (-)-face subunit and loop C Y192 of the principal or (+)-face subunit, whereas three azidonicotinoid probes derivatized only Y192. Both the neonicotinoid and nicotinoid probes labeled Ac-AChBP at only one position at the interface between loop C Y195 and loop E M116. These findings were used to establish structural models of the two AChBP subtypes. In the Ac-AChBP, the neonicotinoids and nicotinoids are nestled in similar bound conformations. Intriguingly, for the Ls-AChBP, the neonicotinoids have two bound conformations that are inverted relative to each other, whereas nicotinoids appear buried in only one conserved conformation as seen for the Ac-AChBP subtype. Accordingly, the subtype selectivity is based on two disparate bound conformations of nicotinic agonists, thereby establishing an atypical concept for neonicotinoid versus nicotinoid selectivity between insect and vertebrate nAChRs.
Tomizawa
Motohiro
M
Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720-3112, USA.
Maltby
David
D
Talley
Todd T
TT
Durkin
Kathleen A
KA
Medzihradszky
Katalin F
KF
Burlingame
Alma L
AL
Taylor
Palmer
P
Casida
John E
JE
D000595:Amino Acid Sequence; D000818:Animals; D001048:Aplysia / Q000378:metabolism; D001665:Binding Sites; D006801:Humans; D007093:Imidazoles / Q000737:chemistry; D008195:Lymnaea / Q000378:metabolism; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D000073943:Neonicotinoids; D018722:Nicotinic Agonists / Q000737:chemistry*; D009574:Nitro Compounds / Q000737:chemistry; D019920:Photoaffinity Labels / Q000737:chemistry; D011487:Protein Conformation / Q000187:drug effects; D011725:Pyridines / Q000737:chemistry; D011978:Receptors, Nicotinic / Q000737:chemistry*; D013843:Thiazines / Q000737:chemistry
D007093:Imidazoles; D000073943:Neonicotinoids; D018722:Nicotinic Agonists; D009574:Nitro Compounds; D019920:Photoaffinity Labels; D011725:Pyridines; D011978:Receptors, Nicotinic; D013843:Thiazines; C082359:imidacloprid; C417209:thiacloprid