beta-Bungarotoxin is a heterodimeric neurotoxin consisting of a phospholipase A, subunit linked by a disulfide bond to a K+ channel binding subunit, which is a member of of the Kunitz protease-inhibitor subfamily. Pur...
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beta-Bungarotoxin is a heterodimeric neurotoxin consisting of a phospholipase A, subunit linked by a disulfide bond to a K+ channel binding subunit, which is a member of of the Kunitz protease-inhibitor subfamily. Purified beta(1)-bungarotoxin was crystallized using microdialysis techniques. The rectangular-shaped crystals are orthorhombic, space group C222(1), with unit-cell dimensions a = 80.7, b = 82.5, c = 56.9 Angstrom. The crystals have a calculated V-m of 2.35 Angstrom(3) Da(-1) for one molecule in the asymmetric unit. This corresponds to a solvent content of 48%. X-ray intensity data were collected to 2.6 Angstrom resolution. The data set is 97.4% complete.
Candoxin, a novel three-finger toxin from Bungarus candidus, is a reversible antagonist of muscle (alphabetagammadelta) but a poorly reversible antagonist of neuronal alpha7 nicotinic acetylcholine receptors. It has a...
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Candoxin, a novel three-finger toxin from Bungarus candidus, is a reversible antagonist of muscle (alphabetagammadelta) but a poorly reversible antagonist of neuronal alpha7 nicotinic acetylcholine receptors. It has a molecular weight of 7344 Da, with 66 amino-acid residues including ten half-cystines. The fifth disulfide bridge is located at the tip of loop I (Cys6-Cys11) instead of in loop II as found in other alpha-neurotoxins. Interestingly, candoxin lacks the segment cyclized by the fifth disulfide bridge at the tip of the middle loop of long-chain neurotoxins, which was reported to be critical for binding to alpha7 receptors. As a first step to determining its three-dimensional structure, candoxin was crystallized by the hanging-drop vapour-diffusion technique in conditions around 1.5 M sodium chloride, 10%(v/v) ethanol. The crystals formed belonged to the hexagonal system, space group P6(2)22, with unit-cell parameters a = 54.88, b = 54.88, c = 75.54 Angstrom, alpha = beta = 90, = 120degrees, and diffract to a resolution of 1.80 Angstrom. The crystallographic asymmetric unit contains one molecule of candoxin, with an estimated solvent content of 44.6%. Attempts to solve these structures by molecular-replacement methods have not been successful and a heavy-atom derivative search has been initiated.
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