title: Three-dimensional structure of the "long" neurotoxin from cobra venom.
abstract: The three-dimensional structure of alpha-cobra-toxin, the "long" neurotoxin from the venom of Naja naja siamensis, has been determined at 2.8-A resolution. Crystals grown as hexagonal needles have space group P6522 with unit cell parameters a = b = 74.59 A, c = 42.89 A; one molecule per asymmetric unit. Phases were determined with a single isomorphous derivative with HgI2 by using the anomalous scattering of the single-site HgI2 molecule to resolve the phase ambiguity. The polypeptide chain folds into three major loops and one tail emerging from a globular head. The protruding long central loop (residues 21-40) is flanked on either side by two shorter loops (residues 4-13 and 44-55); the tail piece (residues 63-71) hangs behind this loop. The molecular conformation is determined by four disulfides in the head and one at the tip of the long loop, by a triple-stranded beta-pleated sheet involving this loop, and by hydrophobic interactions stabilizing the other two loops. The structure of alpha-cobratoxin is compared to that described for the "short" erabutoxin b which shows similar arrangement of structurally and functionally invariant groups.
mesh_terms: D000818:Animals; D003039:Cobra Neurotoxin Proteins; D004220:Disulfides; D004546:Elapid Venoms; D006860:Hydrogen Bonding; D008628:Mercury; D008958:Models, Molecular; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D003039:Cobra Neurotoxin Proteins; D004220:Disulfides; D004546:Elapid Venoms; D008628:Mercury