title: The crystal structures of the calcium-bound con-G and con-T[K7gamma] dimeric peptides demonstrate a metal-dependent helix-forming motif.
abstract: Short peptides that have the ability to form stable alpha-helices in solution are rare, and a number of strategies have been used to produce them, including the use of metal chelation to stabilize folding of the backbone. However, no example exists of a structurally well-defined helix stabilized exclusively through metal ion chelation. Conantokins (con)-G and -T are short peptides that are potent antagonists of N-methyl-D-aspartate receptor channels. While con-G exhibits no helicity alone, it undergoes a structural transition to a helical conformation in the presence of a variety of multivalent cations, especially Mg2+ and Ca2+. This complexation also results in antiparallel dimerization of two peptide helices in the presence of Ca2+, but not Mg2+. A con-T variant, con-T[K7gamma], displays very similar behavior. We have solved the crystal structures of both Ca2+/con-G and Ca2+/con-T [K7gamma] at atomic resolution. These structures clearly show the nature of the metal-dependent dimerization and helix formation and surprisingly also show that the con-G dimer interface is completely different from the con-T[K7gamma] interface, even though the metal chelation is similar in the two peptides. This represents a new paradigm in helix stabilization completely independent of the hydrophobic effect, which we define as the "metallo-zipper."
authors.affiliation: Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Sara E
authors.initials: SE
authors.lastname: Cnudde
authors.forename: Mary
authors.initials: M
authors.lastname: Prorok
authors.forename: Qiuyun
authors.initials: Q
authors.lastname: Dai
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Castellino
authors.forename: James H
authors.initials: JH
authors.lastname: Geiger
mesh_terms: D015055:1-Carboxyglutamic Acid / Q000737:chemistry; D000595:Amino Acid Sequence; D002118:Calcium / Q000737:chemistry*; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D020916:Conotoxins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D036341:Intercellular Signaling Peptides and Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D002135:Calcium-Binding Proteins; D020916:Conotoxins; D036341:Intercellular Signaling Peptides and Proteins; D008978:Mollusk Venoms; D010455:Peptides; C063571:conantokin-T; D015055:1-Carboxyglutamic Acid; C055407:conotoxin GV; D002118:Calcium