Investigation of ligand-binding sites of the acetylcholine receptor using photoactivatable derivatives of neurotoxin II from Naja naja oxiana. |
| |
Authors: | H J Kreienkamp Y N Utkin C Weise J Machold V I Tsetlin F Hucho |
| |
Institution: | Institut für Biochemie, Freie Universit?t Berlin, Germany. |
| |
Abstract: | Several photoaffinity derivatives of neurotoxin II from the venom of the central Asian cobra Naja naja oxiana have been prepared. After reaction of the 125I-labeled derivatives with the nicotinic acetylcholine receptor from electric organ, the alpha-subunit of the nAChR is almost exclusively labeled by the derivative carrying the photoactivatable group in position Lys46. In contrast to this, a reactive group at Lys26 predominantly labels the gamma- and delta-subunits, while the alpha- and beta-subunits incorporate much less radioactivity. Competition experiments with d-tubocurarine show that the gamma-subunit is labeled when this derivative occupies the high affinity d-tubocurarine-binding site, while the delta-subunit is labeled by the toxin bound at the low-affinity d-tubocurarine site. A model is discussed for the orientation of different loops of the toxin molecules in the binding site for agonists and competitive antagonists. |
| |
Keywords: | |
|
|