Analysis of the Structure of <i>Bombyx mori</i> Silk Fibroin by NMR

Asakura, Tetsuo; Okushita, Keiko; Williamson, Michael P.

doi:10.1021/acs.macromol.5b00160

Cited by 183 publications

(267 citation statements)

References 148 publications

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“…Under the fiber formation, Tyr residues stabilize the ends of the forming β-sheet and strengthen the ends of the crystallites. 33 Tyr residues in S. c. ricini silk fibroin were expected to have these functions as well.…”

Section: ■ Resultsmentioning

confidence: 99%

Structural Determination of the Tandem Repeat Motif in Samia cynthia ricini Liquid Silk by Solution NMR

et al. 2015

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The wild silkworm Samia cynthia ricini produces silk fibroin containing polyalanine sequences. The structure of a typical tandem repeat sequence YGGDGG(A) 12 GGAG within S. c. ricini silk fibroin in liquid silk was determined by solution NMR. 13 C, 15 N, and 1 H shifts were assigned from solution NMR spectra for the tandem repeat. TALOS-N was then used to predict the backbone dihedral angles from the chemical shifts. Dihedral angles revealed a well-structured α-helix for the polyalanine region and less stable capping motifs for the N-and Cterminal regions. Consistent with this, the amide proton temperature coefficients of the last glycine in the N-terminal region and the first two glycines in the C-terminal region show more positive values than that of a random coil structure. Thus, the α-helical structure of the polyalanine region of S. c. ricini liquid silk is stabilized by capping motifs.

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Section: ■ Resultsmentioning

confidence: 99%

Structural Determination of the Tandem Repeat Motif in Samia cynthia ricini Liquid Silk by Solution NMR

et al. 2015

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“…Yet a considerable body of literature [49,50,51,52,53,54,55,56] suggests that, prior to coagulation, fibroin is molecularly dissolved in native silk feedstock and adopts a random coil configuration undergoing uniform chain motion [54,55,56], which precludes this conventional explanation. Instead, we propose an alternative hypothesis, based on the native structure of the protein being stabilised by a hydration shell, which can be displaced as a consequence of entropy changes.…”

Section: Discussionmentioning

confidence: 99%

“…An alternative explanation was offered by Jin and Kaplan [43], where the B. mori fibroin was described as a copolymer with alternating hydrophilic and hydrophobic segments, based on the hydropathy index concept of Kyte and Doolitle [48]; flow stress caused the protein to unfold and initiate gelation through hydrophobic interactions. These explanations are not entirely satisfactory, however, as a well-defined tertiary structure appears to be inconsistent with the predominantly disordered or random coil configuration of native fibroin indicated by circular dichroism (CD) [49,50,51,52,53] and nuclear magnetic resonance (NMR) [54,55,56]. In particular, NMR indicated a strong preference for β-turns and fibroin chains exhibiting fast segmental motion typical of a random coil polymer, even in a highly entangled state at the concentration of native silk feedstock within the silkworm.…”

Section: Introductionmentioning

confidence: 99%

The Rheology behind Stress-Induced Solidification in Native Silk Feedstocks

Laity

Holland

2016

IJMS

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The mechanism by which native silk feedstocks are converted to solid fibres in nature has attracted much interest. To address this question, the present work used rheology to investigate the gelation of Bombyx mori native silk feedstock. Exceeding a critical shear stress appeared to be more important than shear rate, during flow-induced initiation. Compositional changes (salts, pH etc.,) were not required, although their possible role in vivo is not excluded. Moreover, after successful initiation, gel strength continued to increase over a considerable time under effectively quiescent conditions, without requiring further application of the initial stimulus. Gelation by elevated temperature or freezing was also observed. Prior to gelation, literature suggests that silk protein adopts a random coil configuration, which argued against the conventional explanation of gelation, based on hydrophilic and hydrophobic interactions. Instead, a new hypothesis is presented, based on entropically-driven loss of hydration, which appears to explain the apparently diverse methods by which silk feedstocks can be gelled.

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“…We note that the structural model of two hydrogen bonds per peptide group for an "amorphous" disordered phase may be confused with the crystalline β-sheet phase as both possess similar density of hydrogen-bonding on average. According to the most recent series of NMR studies 53 , the liquid Silk I structure prior to the native solid silk formation has been identified to be type II β-turns with both inter-and intramolecular hydrogen-bonding, which is a form with a high energy density. Our results further suggest that the noncrystalline structure in native solid silks is highly hydrogenbonded, although this structural form (e.g.…”

Section: T G : Observations and Predictionsmentioning

confidence: 99%

Glass transitions in native silk fibres studied by dynamic mechanical thermal analysis

et al. 2016

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Silks are a family of semi-crystalline structural materials, spun naturally by insects, spiders and even crustaceans. Compared to the characteristic β-sheet crystalline structure in silks, the non-crystalline structure and its composition deserves more attention as it is equally critical to the filaments' high toughness and strength. Here we further unravel the structure-property relationship in silks using Dynamic Mechanical Thermal Analysis (DMTA). This technique allows us to examine the most important structural relaxation event of the disordered structure the disordered structure, the glass transition (GT), in native silk fibres of the lepidopteran Bombyx mori and Antheraea pernyi and the spider Nephila edulis. The measured glass transition temperature Tg, loss tangent tan δ and dynamic storage modulus are quantitatively modelled based on Group Interaction Modelling (GIM). The "variability" issue in native silks can be conveniently explained by the different degrees of structural disorder as revealed by DMTA. The new insights will facilitate a more comprehensive understanding of the structure-property relations for a wide range of biopolymers.

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Analysis of the Structure of Bombyx mori Silk Fibroin by NMR

Cited by 183 publications

References 148 publications

Structural Determination of the Tandem Repeat Motif in Samia cynthia ricini Liquid Silk by Solution NMR

Structural Determination of the Tandem Repeat Motif in Samia cynthia ricini Liquid Silk by Solution NMR

The Rheology behind Stress-Induced Solidification in Native Silk Feedstocks

Glass transitions in native silk fibres studied by dynamic mechanical thermal analysis

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