title: Crystal structure of kappa-bungarotoxin at 2.3-A resolution.
abstract: kappa-Neurotoxins display a very low affinity for neuromuscular receptors, but bind tightly to, and inhibit, nicotinic acetylcholine receptors in neuronal tissue such as the chick ciliary ganglia. In contrast, alpha-neurotoxins bind with high affinity and inhibit nicotinic acetylcholine receptors at the neuromuscular junction. The origin of this difference in specificity has been a long-studied question in the field. Here we report the first crystal structure of a kappa-neurotoxin, kappa-bungarotoxin. Unlike the NMR structure previously reported [Sutcliffe, M. J., Dobson, C. M., & Oswald, R. E. (1992) Biochemistry 31, 2962-2970], the present crystal structure more accurately defines the polypeptide fold and the nature of the interaction between subunits in the active dimer, which is a unique feature of the kappa-neurotoxins. The structure has been refined to R = 19.6% with X-ray diffraction data extending to a resolution of 2.3 A. There are two independent protein molecules (66 amino acid residues each) in the asymmetric unit that are arranged as a dimer with the two subunits related by a rotation of 178.6 degrees. Each subunit consists of three main-chain loops. Three of the five beta-strands of each subunit form an antiparallel beta-sheet which becomes an extended six-stranded antiparallel beta-sheet, by virtue of the approximate 2-fold symmetry of the dimer. The interactions at the dimer interface consist of six main-chain-main-chain hydrogen bonds, as well as three other hydrogen-bonding interactions involving side chains.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: J C
authors.initials: JC
authors.lastname: Dewan
authors.forename: G A
authors.initials: GA
authors.lastname: Grant
authors.forename: J C
authors.initials: JC
authors.lastname: Sacchettini
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002038:Bungarotoxins / Q000737:chemistry*; D005591:Chemical Fractionation; D002851:Chromatography, High Pressure Liquid; D003460:Crystallization; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry; D006860:Hydrogen Bonding; D008628:Mercury / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D011487:Protein Conformation; D011506:Proteins / Q000648:ultrastructure; D012015:Reference Standards; D014501:Uranium / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002038:Bungarotoxins; D004220:Disulfides; D011506:Proteins; D014501:Uranium; D008628:Mercury; D011188:Potassium