The refined crystal structure of alpha-cobratoxin from Naja naja siamensis at 2.4-A resolution |
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Authors: | C Betzel G Lange G P Pal K S Wilson A Maelicke W Saenger |
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Affiliation: | European Molecular Biology Laboratory, Deutsches Elektronen Synchrotron, Hamburg, Federal Republic of Germany. |
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Abstract: | 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. |
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