title: 1H-n.m.r. study of the solution properties and secondary structure of neurotoxin III from the sea anemone Anemonia sulcata.
abstract: The solution properties, secondary structure and global fold of the 27-residue polypeptide neurotoxin III (ATX III), from the sea anemone Anemonia sulcata, have been investigated using high-resolution 1H-n.m.r. spectroscopy. Studies of the concentration dependence of the n.m.r. spectrum indicate that the molecule self-associates in the millimolar concentration range useable for n.m.r. analysis, the association being less pronounced at acidic pH values. The dependence on pH of association implies that electrostatic interactions play a role in this process, while the significant concentration-dependent shifts of the aromatic resonances of Tyr-7 and Trp-13 indicate that hydrophobic interactions also contribute. Individual pKa values have been determined for most ionizable groups in the molecule. Sequence-specific resonance assignments were obtained for all protons using a range of two-dimensional homonuclear-correlated and nuclear-Overhauser-effect (nOe) spectra. The secondary structure of the polypeptide was identified from sequential (i, i+1) and medium-range (i, i+2/3/4) nOe connectivities, NH to C alpha H coupling constants, C alpha H chemical shifts, and the location of slowly exchanging backbone-amide protons. ATX III contains no regular alpha-helix or beta-sheet, consisting instead of a network of reverse turns. nOe connectivities between half-cystine residues are consistent with the disulphide pairings 3-17, 4-11 and 6-22. ATX III has a well-defined structure and appears to lack the disordered loop which, in the longer sea anemone toxins (46-49 residues), may be part of the receptor-binding surface.
authors.affiliation: School of Biochemistry, University of New South Wales, Kensington, Australia.
authors.forename: R S
authors.initials: RS
authors.lastname: Norton
authors.forename: K
authors.initials: K
authors.lastname: Cross
authors.forename: V
authors.initials: V
authors.lastname: Braach-Maksvytis
authors.forename: E
authors.initials: E
authors.lastname: Wachter
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003064:Cnidarian Venoms / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011522:Protons; D012615:Sea Anemones / Q000737:chemistry*; D012996:Solutions
chemical_list: D003064:Cnidarian Venoms; D011522:Protons; D012996:Solutions; C032104:toxin III (Anemonia sulcata)