title: The three-dimensional solution structure of mini-M conotoxin BtIIIA reveals a disconnection between disulfide connectivity and peptide fold.
abstract: Conotoxins are bioactive peptides from the venoms of marine snails and have been divided into several superfamilies based on homologies in their precursor sequences. The M-superfamily conotoxins can be further divided into five branches based on the number of residues in the third loop of the peptide sequence. Recently two M-1 branch conotoxins (tx3a and mr3e) with a C1-C5, C2-C4, C3-C6 disulfide connectivity and one M-2 branch conotoxin (mr3a) with a C1-C6, C2-C4, C3-C5 disulfide connectivity were described. Here we report the disulfide connectivity, chemical synthesis and the three-dimensional NMR structure of the novel 14-residue conotoxin BtIIIA, extracted from the venom of Conus betulinus. It has the same disulfide connectivity as mr3a, which puts it in the M-2 branch conotoxins but has a distinctly different structure from other M-2 branch conotoxins. 105 NOE distance restraints and seven dihedral angle restraints were used for the structure calculations. The three-dimensional structure was determined with CYANA based on torsion angle dynamics and refinement in a water solvent box was carried out with CNS. Fifty structures were calculated and the 20 lowest energy structures superimposed with a RMSD of 0.49±0.16 Å. Even though it has the M-2 branch disulfide connectivity, BtIIIA was found to have a 'flying bird' backbone motif depiction that is found in the M-1 branch conotoxin mr3e. This study shows that conotoxins with the same cysteine framework can have different disulfide connectivities and different peptide folds.
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane QLD 4072, Australia.
authors.forename: Muharrem
authors.initials: M
authors.lastname: Akcan
authors.forename: Ying
authors.initials: Y
authors.lastname: Cao
authors.forename: Fan
authors.initials: F
authors.lastname: Chongxu
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
mesh_terms: D020916:Conotoxins / Q000138:chemical synthesis / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D017510:Protein Folding; D012996:Solutions
chemical_list: D020916:Conotoxins; D004220:Disulfides; D012996:Solutions