title: Crystallization and preliminary X-ray analysis of candoxin, a novel reversible neurotoxin from the Malayan krait Bungarus candidus.
abstract: 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 A, alpha = beta = 90, gamma = 120 degrees, and diffract to a resolution of 1.80 A. 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.
authors.affiliation: Genome Institute of Singapore, Singapore.
authors.forename: Palasingam
authors.initials: P
authors.lastname: Paaventhan
authors.forename: Jeremiah S
authors.initials: JS
authors.lastname: Joseph
authors.forename: Selvanayagam
authors.initials: S
authors.lastname: Nirthanan
authors.forename: Ganapathy
authors.initials: G
authors.lastname: Rajaseger
authors.forename: Ponnampalam
authors.initials: P
authors.lastname: Gopalakrishnakone
authors.forename: Manjunatha R
authors.initials: MR
authors.lastname: Kini
authors.forename: Prasanna R
authors.initials: PR
authors.lastname: Kolatkar
mesh_terms: D000818:Animals; D002038:Bungarotoxins / Q000737:chemistry* / Q000302:isolation & purification; D003460:Crystallization; D018360:Crystallography, X-Ray; D003603:Cytotoxins / Q000737:chemistry* / Q000302:isolation & purification; D009498:Neurotoxins / Q000737:chemistry* / Q000302:isolation & purification; D011994:Recombinant Proteins; D012910:Snake Venoms; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D002038:Bungarotoxins; D003603:Cytotoxins; D009498:Neurotoxins; D011994:Recombinant Proteins; D012910:Snake Venoms; C459604:candoxin