Determinants involved in the affinity of alpha-conotoxins GI and SI for the muscle subtype of nicotinic acetylcholine receptors.
Nicotinic acetylcholine receptors from muscle contain two functionally active and pharmacologically distinct acetylcholine-binding sites located at the alpha/gamma and alpha/delta subunit interfaces. The alpha-conotoxins are competitive antagonists of nicotinic receptors and can be highly site-selective, displaying greater than 10,000-fold differences in affinities for the two acetylcholine-binding sites on a single nicotinic receptor. The higher affinity site for alpha-conotoxins GI, MI, and SI is the alpha/delta site on mouse muscle-derived BC3H-1 receptors. However, alpha-conotoxins GI and MI exhibit higher affinity for the other site (alpha/gamma site) on nicotinic receptors from Torpedo californica electric organ. alpha-Conotoxin SI does not distinguish between the two acetylcholine-binding sites on Torpedo receptors. In this study, alpha-conotoxins [K10H]SI and [K10N]SI displayed wild-type affinity for the two acetylcholine-binding sites on BC3H-1 receptors but a 10-20-fold decrease in apparent affinity at one of the two acetylcholine-binding sites on Torpedo receptors. alpha-Conotoxin [P9K]SI displayed a selective and dramatic increase in the apparent affinity for the alpha/delta site of BC3H-1 receptors and for the alpha/gamma site of Torpedo receptors. alpha-Conotoxin [R9A]GI displayed a reduction in affinity for both acetylcholine-binding sites on BC3H-1 receptors, although the extent of its selectivity for the alpha/delta site was retained. alpha-Conotoxin [R9A]GI also displayed a loss of affinity for the two acetylcholine-binding sites on Torpedo receptors, but its site-selectivity was apparently abolished. These results indicate that positions 9 and 10 in alpha-conotoxins GI and SI are involved in complex species- and subunit-dependent interactions with nicotinic receptors.
Groebe
D R
DR
Department of Pharmacology, School of Medicine, University of Pittsburgh, Pennsylvania 15261, USA.
Gray
W R
WR
Abramson
S N
SN
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002460:Cell Line; D020916:Conotoxins; D004557:Electric Organ / Q000378:metabolism; D051379:Mice; D008978:Mollusk Venoms / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism*; D014101:Torpedo; D014403:Tubocurarine / Q000031:analogs & derivatives / Q000494:pharmacology
D020916:Conotoxins; D008978:Mollusk Venoms; D018733:Nicotinic Antagonists; D010456:Peptides, Cyclic; D011978:Receptors, Nicotinic; C057819:conotoxin SI; C029960:conotoxin GI; C032943:metocurine; D014403:Tubocurarine