title: Three-dimensional structure of conotoxin tx3a: An m-1 branch peptide of the M-superfamily.
abstract: The M-superfamily, one of eight major conotoxin superfamilies found in the venom of the cone snail, contains a Cys framework with disulfide-linked loops labeled 1, 2, and 3 (-CC (1) C (2) C (3) CC-). M-Superfamily conotoxins can be divided into the m-1, -2, -3, and -4 branches, based upon the number of residues located in the third Cys loop between the fourth and fifth Cys residues. Here we provide a three-dimensional solution structure for the m-1 conotoxin tx3a found in the venom of Conus textile. The 15-amino acid peptide, CCSWDVCDHPSCTCC, has disulfide bonds between Cys (1) and Cys (14), Cys (2) and Cys (12), and Cys (7) and Cys (15) typical of the C1-C5, C2-C4, and C3-C6 connectivity pattern seen in m-1 branch peptides. The tertiary structure of tx3a was determined by two-dimensional (1)H NMR in combination with the combined assignment and dynamics algorithm for nuclear magnetic resonance (NMR) applications CYANA program. Input for structure calculations consisted of 62 inter- and intraproton, five phi angle, and four hydrogen bond constraints. The root-mean-square deviation values for the 20 final structures are 0.32 +/- 0.07 and 0.84 +/- 0.11 A for the backbone and heavy atoms, respectively. Surprisingly, the structure of tx3a has a "triple-turn" motif seen in the m-2 branch conotoxin mr3a, which is absent in mr3e, the only other member of the m-1 branch of the M-superfamily whose structure is known. Interestingly, injection of tx3a into mice elicits an excitatory response similar to that of the m-2 branch peptide mr3a, even though the conotoxins have different disulfide connectivity patterns.
authors.affiliation: Department of Chemistry and Biochemistry, Boise State University, Boise, Idaho 83725, USA. owenmcdougal@boisestate.edu
authors.forename: Owen M
authors.initials: OM
authors.lastname: McDougal
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Turner
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Ormond
authors.forename: C Dale
authors.initials: CD
authors.lastname: Poulter
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020916:Conotoxins / Q000737:chemistry*; D052078:Conus Snail / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D020916:Conotoxins; D010455:Peptides