Leu(10) of alpha-conotoxin PnIB confers potency for neuronal nicotinic responses in bovine chromaffin cells.
Two alpha-conotoxins PnIA and PnIB (previously reported as being "mollusc specific") which differ in only two amino acid residues (AN versus LS at residues 10 and 11, respectively), show markedly different inhibition of the neuronal nicotinic acetylcholine receptor response in bovine chromaffin cells, a mammalian preparation. Whereas alpha-conotoxin PnIB completely inhibits the nicotine-evoked catecholamine release at 10 microM, with IC(50) = 0.7 microM, alpha-conotoxin PnIA is some 30-40 times less potent. Two peptide analogues, [A10L]PnIA and [N11S]PnIA were synthesized to investigate the extent to which each residue contributes to activity. [A10L]PnIA (IC(50) = 2.0 microM) completely inhibits catecholamine release at 10 microM whereas [N11S]PnIA shows little inhibition. In contrast, none of the peptides inhibit muscle-type nicotinic responses in the rat hemi-diaphragm preparation. We conclude that the enhanced potency of alpha-conotoxin PnIB over alpha-conotoxin PnIA in the neuronal-type nicotinic response is principally determined by the larger, more hydrophobic leucine residue at position 10 in alpha-conotoxin PnIB.
Broxton
N
N
Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3052, Australia.
Miranda
L
L
Gehrmann
J
J
Down
J
J
Alewood
P
P
Livett
B
B
D000595:Amino Acid Sequence; D000818:Animals; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D018680:Cholinergic Antagonists / Q000494:pharmacology*; D019439:Chromaffin Cells / Q000187:drug effects* / Q000378:metabolism; D020916:Conotoxins / Q000737:chemistry / Q000494:pharmacology*; D003964:Diaphragm / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D009842:Oligopeptides / Q000138:chemical synthesis / Q000494:pharmacology*; D010791:Phrenic Nerve / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000378:metabolism
D002395:Catecholamines; D018680:Cholinergic Antagonists; D020916:Conotoxins; D009842:Oligopeptides; D011978:Receptors, Nicotinic; C089038:alpha-conotoxin PnIA; C089039:alpha-conotoxin PnIB; D009638:Norepinephrine