title: Conantokin-P, an unusual conantokin with a long disulfide loop.
abstract: The conantokins are a family of Conus venom peptides (17-27AA) that are N-methyl-d-aspartate (NMDA) receptor antagonists. Conantokins lack disulfide bridges (six out of seven previously characterized peptides are linear), but contain multiple residues of gamma-carboxyglutamate. These post-translationally modified amino acids confer the largely helical structure of conantokins by coordinating divalent metal ions. Here, we report that a group of fish-hunting cone snails, Conus purpurascens and Conus ermineus, express a distinctive branch of the conantokin family in their venom ducts. Two novel conantokins, conantokin-P (Con-P) and conantokin-E (Con-E) are 24AA long and contain five gamma-carboxyglutamate residues. These two peptides are characterized by a long disulfide loop (12 amino acids including two Gla residues between the Cys residues). The oxidative folding studies of Con-P revealed that the formation of the disulfide bond proceeded significantly faster in the presence of Ca(++) ions. Circular dichroism suggested that Con-P is less helical than other previously characterized conantokins. Con-P blocks NMDA receptors containing NR2B subunit with submicromolar potency. Furthermore, the subtype-selectivity for different NR2 subunits differs from that of the previously characterized conantokins. Our results suggest that different branches of the phylogenetic tree of cone snails have evolved distinct groups of conantokins, each with its own unique biochemical features.
authors.affiliation: Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.
authors.forename: Konkallu Hanumae
authors.initials: KH
authors.lastname: Gowd
authors.forename: Vernon
authors.initials: V
authors.lastname: Twede
authors.forename: Maren
authors.initials: M
authors.lastname: Watkins
authors.forename: K S
authors.initials: KS
authors.lastname: Krishnan
authors.forename: Russell W
authors.initials: RW
authors.lastname: Teichert
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Bulaj
authors.forename: Baldomero M
authors.initials: BM
authors.lastname: Olivera
mesh_terms: D015055:1-Carboxyglutamic Acid / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D020916:Conotoxins / Q000138:chemical synthesis / Q000737:chemistry; D052078:Conus Snail / Q000502:physiology*; D004247:DNA / Q000032:analysis; D004220:Disulfides / Q000737:chemistry*; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000737:chemistry*; D010802:Phylogeny; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry
chemical_list: D020916:Conotoxins; D004220:Disulfides; D008978:Mollusk Venoms; C121001:NR2B NMDA receptor; D016194:Receptors, N-Methyl-D-Aspartate; C532519:conantokin-E; C532518:conantokin-P; D015055:1-Carboxyglutamic Acid; D004247:DNA