The refined crystal structure of alpha-cobratoxin from Naja naja siamensis at 2.4-A resolution.
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The crystal structure of the "long" alpha-neurotoxin alpha-cobratoxin was refined to an R-factor of 19.5% using 3271 x-ray data to 2.4-A resolution. The polypeptide chain forms three loops, I, II, III, knotted together by four disulfide bridges, with the most prominent, loop II, containing another disulfide close to its lower tip. Loop I is stabilized by one beta-turn and two beta-sheet hydrogen bonds; loop II by eight beta-sheet hydrogen bonds, with the tip folded into two distorted right-handed helical turns stabilized by two alpha-helical and two beta-turn hydrogen bonds; and loop III by hydrophobic interactions and one beta-turn. Loop II and one strand of loop III form an antiparallel triple-pleated beta-sheet, and tight anchoring of the Asn63 side chain fixes the tail segment. In the crystal lattice, the alpha-cobratoxin molecules dimerize by beta-sheet formation between strands 53 and 57 of symmetry-related molecules. Because such interactions are found also in a cardiotoxin and alpha-bungarotoxin, this could be of importance for interaction with acetylcholine receptor. (+info)
A novel fluorescent alpha-conotoxin for the study of alpha7 nicotinic acetylcholine receptors.
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The short-neurotoxin-binding regions on the alpha-chain of human and Torpedo californica acetylcholine receptors.
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The continuous regions for short-neurotoxin binding on the alpha-chains of Torpedo californica (electric ray) and human acetylcholine receptors (AChR) were localized by reaction of 125I-labelled cobrotoxin (Cot) and erabutoxin b (Eb) with synthetic overlapping peptides spanning the entire extracellular part of the respective alpha-chains. On Torpedo AChR, five Cot-binding regions were found to reside within peptides alpha 1-16, alpha 23-38/alpha 34-49 overlap, alpha 100-115, alpha 122-138 and alpha 194-210. The Eb-binding regions were localized within peptides alpha 23-38/alpha 34-49/alpha 45-60 overlap, alpha 100-115 and alpha 122-138. The main binding activity for both toxins resided within region alpha 122-138. In previous studies we had shown that the binding of long alpha-neurotoxins [alpha-bungarotoxin (Bgt) and cobratoxin (Cbt)] involved the same regions on Torpedo AChR as well as an additional region within residues alpha 182-198. Thus region alpha 182-198, which is the strongest binding region for long neurotoxins on Torpedo AChR, was not a binding region for short neurotoxins. On human AChR, peptide alpha 122-138 possessed the highest activity with both toxins, and lower activity was found in the overlap alpha 23-38/alpha 34-49/alpha 45-60 and in peptide alpha 194-210. In addition, peptides alpha 100-115 and alpha 56-71 showed strong and medium binding activities to Eb, but low activity to Cot, whereas peptide alpha 1-16 exhibited low binding to Cot and no binding to Eb. Comparison with previous studies indicated that, for human AChR, the binding regions of short and long neurotoxins were essentially the same. The finding that the region within residues alpha 122-138 of both human and Torpedo AChR possessed the highest binding activity with short neurotoxins indicated that this region constitutes a universal binding site for long and short neurotoxins on AChR from various species. (+info)