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Tetsuo Asakura – One of the best experts on this subject based on the ideXlab platform.

  • Characterization of a Ca binding-amphipathic silk-like protein and peptide with the sequence (Glu)8(Ala-Gly-Ser-Gly-Ala-Gly)4 with potential for bone repair
    Soft Matter, 2012
    Co-Authors: Aya Nagano, Hirohiko Sato, Yumi Tanioka, Yasumoto Nakazawa, David W. Knight, Tetsuo Asakura

    Abstract:

    Bombyx mori silk fibroin with the main sequence (Ala-Gly-Ser-Gly-Ala-Gly)n is a promising scaffold for bone regeneration not only on account of its excellent mechanical property as a structural matrix, but also for its slow biodegradability with adequate control of hydroxyapatite (HAP) deposition. Seeking to develop a material that might stimulate bone regeneration, we prepared a recombinant calcium binding-amphipathic silk-like protein [(Glu)8(Ala-Gly-Ser-Gly-Ala-Gly)4]4 by expression in E. coli. We also prepared the homologous peptide (Glu)8(Ala-Gly-Ser-Gly-Ala-Gly)4 by solid phase synthesis. The poly-L-glutamic acid was introduced into both protein and peptide because this sequence is involved in HAP-nucleating domains of bone sialoprotein. The recombinant protein was shown to bind relatively large quantities of Ca2+ ions in solution by a spectrophotometric assay and in the solid state by X-ray photoelectron spectroscopy. Changes in the electronic structure and local conformation of the peptide resulting from Ca2+ binding were studied using 13C solution NMR, especially 13C chemical shifts. We obtained evidence that Ca2+ bound to the poly-L-glutamic acid domains but not to the predominantly hydrophobic (Ala-Gly-Ser-Gly-Ala-Gly)4 domains. A remarkable conformational change induced by adsorption of the synthetic peptide on the HAP surface was also demonstrated using 13C solid state NMR.

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  • Local conformation of serine residues in a silk model peptide, (Ala–Gly–Ser–Gly–Ala–Gly) 5 , studied with solid-state NMR:REDOR
    Polymer Journal, 2010
    Co-Authors: Yu Suzuki, Tetsuo Asakura

    Abstract:

    Local conformation of serine residues in a silk model peptide, (Ala–Gly–Ser–Gly–Ala–Gly) 5 , studied with solid-state NMR:REDOR

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  • Determination of the torsion angles of alanine and glycine residues of model compounds of spider silk (AGG)_10 using solid-state NMR methods
    Journal of Biomolecular NMR, 2003
    Co-Authors: Jun Ashida, Kosuke Ohgo, Kohei Komatsu, Ayumi Kubota, Tetsuo Asakura

    Abstract:

    Spiders synthesize several kinds of silk fibers. In the primary structure of spider silk, one of the major ampullate (dragline, frame) silks, spidroin 1, and flagelliform silk (core fibers of adhesive spiral), there are common repeated X-Gly-Gly (X = Ala, Leu, Pro, Tyr, Glu, and Arg) sequences, which are considered to be related to the elastic character of these fibers. In this paper, two dimensional spin diffusion solid-state NMR under off magic angle spinning (OMAS), ^13C chemical shift contour plots, and Rotational Echo DOuble Resonance (REDOR) were applied to determine the torsion angles of one Ala and two kinds of Gly residues in the Ala-Gly-Gly sequence of ^13C=O isotope-labeled (Ala-Gly-Gly)_10. The torsion angles were determined to be (φ, ψ) = (−90°, 150° ) within an experimental error of ±10° for each residue. This conformation is characterized as 3_1 helix which is in agreement with the structure proposed from the X-ray powder diffraction pattern of poly(Ala-Gly-Gly). The 3_1 helix of (Ala-Gly-Gly)_10 does not change by formic acid treatment although (Ala-Gly)_15 easily changes from the silk I conformation (the structure of Bombyx mori silk fibroin before spinning in the solid state) to silk II conformation (the structure of the silk fiber after spinning) by such treatment. Thus, the 3_1 helix conformation of (Ala-Gly-Gly)_10 is considered very stable. Furthermore, the torsion angles of the 16th Leu residue of (Leu-Gly-Gly)_10 were also determined as (φ, ψ) = (−90°, 150° ) and this peptide is also considered to take 3_1 helix conformation.

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Yasumoto Nakazawa – One of the best experts on this subject based on the ideXlab platform.

  • Characterization of a Ca binding-amphipathic silk-like protein and peptide with the sequence (Glu)8(Ala-Gly-Ser-Gly-Ala-Gly)4 with potential for bone repair
    Soft Matter, 2012
    Co-Authors: Aya Nagano, Hirohiko Sato, Yumi Tanioka, Yasumoto Nakazawa, David W. Knight, Tetsuo Asakura

    Abstract:

    Bombyx mori silk fibroin with the main sequence (Ala-Gly-Ser-Gly-Ala-Gly)n is a promising scaffold for bone regeneration not only on account of its excellent mechanical property as a structural matrix, but also for its slow biodegradability with adequate control of hydroxyapatite (HAP) deposition. Seeking to develop a material that might stimulate bone regeneration, we prepared a recombinant calcium binding-amphipathic silk-like protein [(Glu)8(Ala-Gly-Ser-Gly-Ala-Gly)4]4 by expression in E. coli. We also prepared the homologous peptide (Glu)8(Ala-Gly-Ser-Gly-Ala-Gly)4 by solid phase synthesis. The poly-L-glutamic acid was introduced into both protein and peptide because this sequence is involved in HAP-nucleating domains of bone sialoprotein. The recombinant protein was shown to bind relatively large quantities of Ca2+ ions in solution by a spectrophotometric assay and in the solid state by X-ray photoelectron spectroscopy. Changes in the electronic structure and local conformation of the peptide resulting from Ca2+ binding were studied using 13C solution NMR, especially 13C chemical shifts. We obtained evidence that Ca2+ bound to the poly-L-glutamic acid domains but not to the predominantly hydrophobic (Ala-Gly-Ser-Gly-Ala-Gly)4 domains. A remarkable conformational change induced by adsorption of the synthetic peptide on the HAP surface was also demonstrated using 13C solid state NMR.

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  • the role of irregular unit gaas on the secondary structure of bombyx mori silk fibroin studied with 13c cp mas nmr and wide angle x ray scattering
    Protein Science, 2002
    Co-Authors: Tetsuo Asakura, Rena Sugino, Tatsushi Okumura, Yasumoto Nakazawa

    Abstract:

    Bombyx mori silk fibroin is a fibrous protein whose fiber is extremely strong and tough, although it is produced by the silkworm at room temperature and from an aqueous solution. The primary structure is mainly Ala-Gly alternative copolypeptide, but Gly-Ala-Ala-Ser units appear frequently and periodically. Thus, this study aims at elucidating the role of such Gly-Ala-Ala-Ser units on the secondary structure. The sequential model peptides containing Gly-Ala-Ala-Ser units selected from the primary structure of B. mori silk fibroin were synthesized, and their secondary structure was studied with 13C CP/MAS NMR and wide-angle X-ray scattering. The 13C isotope labeling of the peptides and the 13C conformation-dependent chemical shifts were used for the purpose. The Ala-Ala units take antiparallel β-sheet structure locally, and the introduction of one Ala-Ala unit in (Ala-Gly)15 chain promotes dramatical structural changes from silk I (repeated β-turn type II structure) to silk II (antiparallel β-sheet structure). Thus, the presence of Ala-Ala units in B. mori silk fibroin chain will be one of the inducing factors of the structural transition for silk fiber formation. The role of Tyr residue in the peptide chain was also studied and clarified to induce “locally nonordered structure.”

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Çetin Tasseven – One of the best experts on this subject based on the ideXlab platform.

  • Thermophysical Properties of Anti-Parallel β-Sheets with Bombyx mori Silk Nanostructures [Gly-Ser-Gly-Ala-Gly-Ala]n and [Gly-Ala]n
    Materials Science Forum, 2016
    Co-Authors: Baki Aksakal, Seçkin D. Günay, Ünsal Akdere, Tahir Çağın, Çetin Tasseven

    Abstract:

    Thermal expansion of anti-parallel beta pleated sheets with Bombyx mori silk nanostructures [Gly-Ser-Gly-Ala-Gly-Ala]n and commonly used model of [Gly-Ala]n have been investigated through molecular dynamics (MD) simulation calculations in conjunction with interatomic interactions modeled by CHARMM force field method between the temperature range of 300K-700K. Preliminary results indicate significant differences on thermal expansion of two structures that was observed on directions of chain and the direction perpendicular to plates.

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  • Thermomechanical Properties of Anti-Parallel β-Sheets with Bombyx mori Silk Nanostructures [Gly-Ser-Gly-Ala-Gly-Ala]n and [Gly-Ala]n
    Materials Science Forum, 2016
    Co-Authors: Seçkin D. Günay, Baki Aksakal, Ünsal Akdere, Tahir Çağın, Çetin Tasseven

    Abstract:

    Thermal expansion of anti-parallel beta pleated sheets with Bombyx mori silk nanostructures [Gly-Ser-Gly-Ala-Gly-Ala]n and commonly used model of [Gly-Ala]n have been investigated through molecular dynamics (MD) simulation calculations in conjunction with interatomic interactions modeled by CHARMM force field method between the temperature range of 300K-700K. Preliminary results indicate significant differences on thermal expansion of two structures that was observed on directions of chain and the direction perpendicular to plates.

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