2frb | pdb_00002frb
NMR structure of the alpha-conotoxin GI (ASN4)-benzoylphenylalanine derivative
Structural highlights
Function[CA1A_CONGE] Alpha-conotoxins act on postsynaptic membranes, they bind to the nicotinic acetylcholine receptors (nAChR) and thus inhibit them. The higher affinity site for alpha-conotoxin GI is the alpha/delta site on mouse muscle-derived BC3H-1 receptor, and the other site (alpha/gamma site) on nicotinic receptors from Torpedo californica electric organ. Publication Abstract from PubMedalpha-Conotoxins are small peptides from cone snail venoms that function as nicotinic acetylcholine receptor (nAChR)-competitive antagonists differentiating between nAChR subtypes. Current understanding about the mechanism of these selective interactions is based largely on mutational analyses, which identify amino acids in the toxin and nAChR that determine the energetics of ligand binding. To identify regions of the nAChR involved in alpha-conotoxin binding by use of photoactivated cross-linking, two benzoylphenylalanine (Bpa) analogs of alpha-conotoxin GI, GI(Bpa12) and GI(Bpa4), were synthesized by replacing the respective residues with Bpa, and their (1)H-NMR structures were determined. Both analogs preserved the GI conformation, but only GI(Bpa12) displaced (125)I-labeled GI from the Torpedo californica nAChR. (125)I-labeled GI(Bpa12) bound to two sites on the receptor (K(d) 13 and 1800 nM), and on UV irradiation specifically photolabeled the alpha, gamma and delta subunits. Photolabeling sites were mapped by selective proteolysis and enzymatic deglycosylation, combined with SDS/PAGE, HPLC and Edman degradation. In the alpha subunit, cobratoxin-inhibited incorporation was limited to the 22-kDa fragment beginning at alphaSer173 and containing the agonist-binding site segment C. In the gamma subunit, radioactivity was localized to two distinct peptides containing agonist-binding site segments F and D: nonglycosylated 24-kDa and glycosylated 13-kDa fragments starting at gammaAla167 and gammaAla49, respectively. The labeling of these fragments is discussed in terms of a model of GI(Bpa12) bound to the extracellular domain of the Torpedo nAChR homology model derived from the cryo-electron microscopy structure of Torpedo marmorata nAChR and X-ray crystal structures of snail acetylcholine-binding protein complexes with agonists and antagonists. alpha-Conotoxin GI benzoylphenylalanine derivatives. (1)H-NMR structures and photoaffinity labeling of the Torpedo californica nicotinic acetylcholine receptor.,Kasheverov IE, Chiara DC, Zhmak MN, Maslennikov IV, Pashkov VS, Arseniev AS, Utkin YN, Cohen JB, Tsetlin VI FEBS J. 2006 Apr;273(7):1373-88. PMID:16689926[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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