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Soft metal ions, Cd(II) and Hg(II), induce triple-stranded α-helical assembly and folding of a de novo designed peptide in their trigonal geometries

Published online by Cambridge University Press:  01 July 2000

XIANGQUN LI
Affiliation:
Biomolecular Engineering Research Institute, Suita, Osaka 565-0874, Japan
KAZUO SUZUKI
Affiliation:
Biomolecular Engineering Research Institute, Suita, Osaka 565-0874, Japan
KENJI KANAORI
Affiliation:
Department of Polymer Science & Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
KUNIHIKO TAJIMA
Affiliation:
Department of Polymer Science & Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
AYUMI KASHIWADA
Affiliation:
Biomolecular Engineering Research Institute, Suita, Osaka 565-0874, Japan
HIDEKAZU HIROAKI
Affiliation:
Biomolecular Engineering Research Institute, Suita, Osaka 565-0874, Japan
DAISUKE KOHDA
Affiliation:
Biomolecular Engineering Research Institute, Suita, Osaka 565-0874, Japan
TOSHIKI TANAKA
Affiliation:
Biomolecular Engineering Research Institute, Suita, Osaka 565-0874, Japan
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Abstract

We previously reported the de novo design of an amphiphilic peptide [YGG(IEKKIEA)4] that forms a native-like, parallel triple-stranded coiled coil. Starting from this peptide, we sought to regulate the assembly of the peptide by a metal ion. The replacement of the Ile18 and Ile22 residues with Ala and Cys residues, respectively, in the hydrophobic positions disrupted of the triple-stranded α-helix structure. The addition of Cd(II), however, resulted in the reconstitution of the triple-stranded α-helix bundle, as revealed by circular dichroism (CD) spectroscopy and sedimentation equilibrium analysis. By titration with metal ions and monitoring the change in the intensity of the CD spectra at 222 nm, the dissociation constant Kd was determined to be 1.5 ± 0.8 μM for Cd(II). The triple-stranded complex formed by the 113Cd(II) ion showed a single 113Cd NMR resonance at 572 ppm whose chemical shift was not affected by the presence of Cl ions. The 113Cd NMR resonance was connected with the βH protons of the cysteine residue by 1H–113Cd heteronuclear multiple quantum correlation spectroscopy. These NMR results indicate that the three cysteine residues are coordinated to the cadmium ion in a trigonal-planar complex. Hg(II) also induced the assembly of the peptide into a triple-stranded α-helical bundle below the Hg(II)/peptide ratio of 1/3. With excess Hg(II), however, the α-helicity of the peptide was decreased, with the change of the Hg(II) coordination state from three to two. Combining this construct with other functional domains should facilitate the production of artificial proteins with functions controlled by metal ions.

Type
Research Article
Copyright
2000 The Protein Society

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