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

Suzuki, Yuichi; Kawanishi, Shuto; Yamazaki, Toshimasa; Aoki, Akihiro; Saitô, Hitoshi; Asakura, Tetsuo

doi:10.1021/acs.macromol.5b01717

Cited by 20 publications

(15 citation statements)

References 33 publications

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“…The native silk fiber was β -sheet-rich whereas the LF aq as-cast film was α -helix-rich. These results are consistent with previous work [12,22], since S. c. ricini LF is known to have a well-structured α -helical conformation in the PA region [27]. This result was well supported by FTIR as shown in the typically α -helix-rich FTIR spectrum of the LF aq as-cast film in Figure 2.…”

Section: Resultssupporting

confidence: 92%

“…Similar to the PA sequences in S. c. ricini and other native wild SF, X-ray diffraction, and infrared, Raman and solid-state NMR spectroscopy studies [15,16,17,18,19,20,21,22,23,24] have shown the (GAGAGS) n repeat sequence regions in B. mori silk SF to primarily contribute to the formation of β -sheets [17,19,20,21,25,26]. In addition, the two kinds of SF have other structures such as α -helix and random coil [21,27].…”

Section: Introductionmentioning

confidence: 99%

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Aggregation State of Residual α-Helices and Their Influence on Physical Properties of S. c. ricini Native Fiber

et al. 2019

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Formation of the α-helical conformation in the poly-l-alanine (PA) sequence regions, subsequent structural transition to β-sheet during natural spinning, and presence of residual α-helices in Samia cynthia ricini (S. c. ricini) native silk fiber have been experimentally proven. However, the aggregation state of the residual α-helices, and their influence on the mechanical deformation behavior in native fiber remain unclear. Here we show that the α-helices form an ordered aggregation state with a hexagonal packing in the aqueous solution, some of which remain during natural spinning. X-ray scattering and differential scanning calorimetry (DSC) analyses revealed occurrence of a structural transition of the residual α-helices to the β-sheet structure, accompanied by disappearance of the plateau region in the force-strain curve, due to heat-treatment at ~220 °C. On the basis of X-ray scattering before and after tensile stretching of S. c. ricini native silk, a direct connection between the plateau region and the α-helix to β-sheet structural transition was confirmed. Our findings demonstrate the importance of the PA sequence regions in fiber structure formation and their influence on the tensile deformation behavior of S. c. ricini silk, features believed to be essentially similar in other saturniid silks. We strongly believe the residual ordered α-helices to be strategically and systematically designed by S. c. ricini silkworms to impart flexibility in native silk fiber. We anticipate that these knowledge forms a basis for fruitful strategies in the design and development of amino acid sequences for artificial silks with desired mechanical properties.

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Section: Resultssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Aggregation State of Residual α-Helices and Their Influence on Physical Properties of S. c. ricini Native Fiber

et al. 2019

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“…In contrast, the longer polyalanine region in E. australis repetitive domain leads to the formation of helical structure 55 . The helical structure of the polyalanine in E. australis is also similar to the helical structure of a long polyalanine region (10–14 alanine residues) in Samia cynthia ricini 56 . In the case of E. australis spidroins, hydrophobicity of the repetitive domain and hydrophilicity of the C-terminal domain cause to form micelle-like structure 42 .…”

Section: Discussionmentioning

confidence: 55%

Conformation and dynamics of soluble repetitive domain elucidates the initial β-sheet formation of spider silk

Oktaviani

Matsugami²,

Malay

et al. 2018

Nat Commun

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The β-sheet is the key structure underlying the excellent mechanical properties of spider silk. However, the comprehensive mechanism underlying β-sheet formation from soluble silk proteins during the transition into insoluble stable fibers has not been elucidated. Notably, the assembly of repetitive domains that dominate the length of the protein chains and structural features within the spun fibers has not been clarified. Here we determine the conformation and dynamics of the soluble precursor of the repetitive domain of spider silk using solution-state NMR, far-UV circular dichroism and vibrational circular dichroism. The soluble repetitive domain contains two major populations: ~65% random coil and ~24% polyproline type II helix (PPII helix). The PPII helix conformation in the glycine-rich region is proposed as a soluble prefibrillar region that subsequently undergoes intramolecular interactions. These findings unravel the mechanism underlying the initial step of β-sheet formation, which is an extremely rapid process during spider silk assembly.

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“…There are mainly two kinds of Ala residues in the liquid silk of S. c. ricini stored in the middle silk glands, i.e., Ala residues in the polyalanine sequences (A) n (n = 12, 13) and the isolated Ala residue [ 41 ]. The polyalanine sequences take α-helical conformation, whereas the isolated Ala residues take random coil in the liquid silk [ 39 , 40 , 42 , 43 , 44 , 45 , 46 , 47 ]. Therefore, the chemical shifts of the Ala main peaks of S. c. ricini liquid silk are a good chemical shift reference for α-helix, and the small peaks are a good chemical shift reference for the random coil.…”

Section: Structure Of Silk Stored In the Middle Silk Gland Of B Mori Silkwormmentioning

confidence: 99%

Structure of Silk I (Bombyx mori Silk Fibroin before Spinning) -Type II β-Turn, Not α-Helix-

Asakura

2021

Molecules

Self Cite

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Recently, considerable attention has been paid to Bombyx mori silk fibroin by a range of scientists from polymer chemists to biomaterial researchers because it has excellent physical properties, such as strength, toughness, and biocompatibility. These appealing physical properties originate from the silk fibroin structure, and therefore, structural determinations of silk fibroin before (silk I) and after (silk II) spinning are a key to make wider applications of silk. There are discrepancies about the silk I structural model, i.e., one is type II β-turn structure determined using many solid-state and solution NMR spectroscopies together with selectively stable isotope-labeled model peptides, but another is α-helix or partially α-helix structure speculated using IR and Raman methods. In this review, firstly, the process that led to type II β-turn structure by the authors was introduced in detail. Then the problems in speculating silk I structure by IR and Raman methods were pointed out together with the problem in the assignment of the amide I band in the spectra. It has been emphasized that the conformational analyses of proteins and peptides from IR and Raman studies are not straightforward and should be very careful when the proteins contain β-turn structure using many experimental data by Vass et al., (Chem. Rev., 2003, 103, 1917–1954). In conclusion, the author emphasized here that silk I structure should be type II β-turn, not α-helix.

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

Cited by 20 publications

References 33 publications

Aggregation State of Residual α-Helices and Their Influence on Physical Properties of S. c. ricini Native Fiber

Aggregation State of Residual α-Helices and Their Influence on Physical Properties of S. c. ricini Native Fiber

Conformation and dynamics of soluble repetitive domain elucidates the initial β-sheet formation of spider silk

Structure of Silk I (Bombyx mori Silk Fibroin before Spinning) -Type II β-Turn, Not α-Helix-

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