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Lynn W Jelinski - One of the best experts on this subject based on the ideXlab platform.
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Rotational-echo Double-resonance in Complex Biopolymers: a Study of Nephila clavipes Dragline Silk
Journal of Biomolecular NMR, 1998Co-Authors: Carl A. Michal, Lynn W JelinskiAbstract:Rotational-Echo Double-Resonance (REDOR) NMR on strategically 13C and 15N labeled samples is used to study the conformation of the LGXQ (X = S, G, or N) motif in the major ampullate gland dragline silk from the spider Nephila clavipes. A method is described for calculating REDOR dephasing curves suitable for background subtractions, using probability distributions of nitrogen atoms surrounding a given carbon site, which are developed from coordinates in the Brookhaven Protein Data Bank. The validity of the method is established by comparison to dephasings observed from natural abundance 13C peaks for G and A. Straightforward fitting of universal REDOR dephasing curves to the background corrected peaks of interest provide results which are not self-consistent, and a more sophisticated analysis is developed which better accounts for 15N labels which have scrambled from the intended positions. While there is likely some heterogeneity in the structures formed by the LGXQ sequences, the data indicate that they all form compact turn-like structures.
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conformation of the polyalanine repeats in minor ampullate gland silk of the spider Nephila clavipes
Macromolecules, 1997Co-Authors: Oskar Liivak, Randolph V Lewis, Anthony Flores, Lynn W JelinskiAbstract:Solid state 13C NMR is used to identify the conformation of alanine residues in minor ampullate gland silk from Nephila clavipes and in a genetically engineered protein based on the consensus sequence of MaSp2, a protein present in low concentrations in major ampullate gland silk. The results of the NMR on minor ampullate gland silk are compared to previous NMR data on major ampullate gland silk, and the results on the genetically engineered protein are compared to previous NMR data on the gland fibroin from the major ampullate gland. Differences in the secondary structure of major and minor ampullate gland silk are correlated with mechanical properties. The alanine residues of major ampullate gland silk have previously been shown to consist almost entirely of β-sheet conformations. In contrast, the conformations of the alanine residues of minor ampullate gland silk are more heterogeneous, with a larger fraction of the alanine residues in non-β-sheet conformations. It is hypothesized that these non-β-shee...
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13c nmr of Nephila clavipes major ampullate silk gland
Biophysical Journal, 1996Co-Authors: David H Hijirida, D. B. Zax, Carl A. Michal, S Wong, Lynn W JelinskiAbstract:The major ampullate glands of the spider Nephila clavipes contain approximately 0.2 microliter each of a highly concentrated (approximately 50%) solution of silk fibroin. Therefore, the reservoir of silk in these glands presents an ideal opportunity to observe prefolded conformations of a protein in its native state. To this end, the structure and conformation of major ampullate gland silk fibroin within the glands of the spider N. clavipes were examined by 13C NMR spectroscopy. These results were compared to those from silk protein first drawn from the spinneret and then denatured. The 13C NMR chemical shifts, along with infrared and circular dichroism data, suggest that the silk fibroin in the glands exists in dynamically averaged helical conformations. Furthermore, there is no evidence of proline residues in U-(13)C-D-glucose-labeled silk. This transient prefolded "molten fibril" state may correspond to the silk I form found in Bombyx mori silk. There is no evidence of the final beta-sheet structure in the ampullate gland silk fibroin before final silk processing. However, the conformation of silk in the glands appears to be in a highly metastable state, as plasticization with water produces the beta-sheet structure. Therefore, the ducts connecting the ampullate glands to the spinnerets play a larger role in silk processing than previously thought.
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Presence of phosphorus in Nephila clavipes dragline silk
Biophysical journal, 1996Co-Authors: Carl A. Michal, Alexandra H. Simmons, B. G. M. Chew, D. B. Zax, Lynn W JelinskiAbstract:Solid-state 31P-NMR of Nephila clavipes dragline silk indicates the presence of phosphorus in at least two chemically distinct environments. Amino acid analyses of acid-hydrolyzed silk confirm the presence of phosphotyrosine as one of the phosphorus-containing components. The unusual chemical shift (18.9 ppm downfield from 85% H3PO4), proton chemical shift, and acid lability of a second component suggest that it is part of a strained five-membered cyclic phosphate that might be found on a beta-D-ribose. The five-membered cyclic phosphate is not removed from the silk fibers by exhaustive aqueous extraction. It is absent in nascent silk fibroin from the glands, suggesting that its formation is part of the fiber processing that occurs in the ducts leading to the spinnerets. High-resolution NMR spectra of silk dissolved in propionic acid/12 N HCl (50:50 v/v) show five phosphorus sites assigned to phosphorylated tyrosine residues, phosphorylated serine residues, inorganic phosphate, and two hydrolysis products of the cyclic phosphate compound. The observed posttranslational phosphorylation may be important in the processing and modulation of the physical properties of dragline silk.
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solid state 13c nmr of Nephila clavipes dragline silk establishes structure and identity of crystalline regions
Macromolecules, 1994Co-Authors: Alexandra Simmons, Lynn W JelinskiAbstract:13 C CP/MAS NMR spectra of dragline silk of Nephila clavipes show unambiguously that the alanine residues are present in the β-sheet conformation. Proton T 1ρ data show that the heterogeneities in the silk must be small. Two motional environments have been detected for the alanine residues. These data verify that dragline silk is composed of crystalline regions of polyalanine β-sheets in a more flexible matrix
Michel Pezolet - One of the best experts on this subject based on the ideXlab platform.
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conformation and orientation of proteins in various types of silk fibers produced by Nephila clavipes spiders
Biomacromolecules, 2009Co-Authors: Marieeve Rousseau, Thierry Lefevre, Michel PezoletAbstract:Silk fibers harvested from the web, cocoon, and prey wrapping of the spider Nephila clavipes have been studied by polarized Raman spectromicroscopy. The technique is efficient to differentiate the various types of silk by probing monofilaments produced by the major ampullate (MA), minor ampullate (MI), cylindriform, flagelliform, and aciniform glands. The spectra show that the MA, MI, and cylindriform silks belong to the same structural class and are composed of highly oriented β-sheets (35−37%) with other slightly oriented secondary structures. Spectral markers of particular motifs involved in the β-sheets have been identified. The flagelliform silk represents a second, very peculiar structural class. It displays a heterogeneous disordered conformation without any preferential orientation. Such characteristics certainly play a role in the large extensibility of this silk. The aciniform silk represents a third class of silk dominated by moderately oriented β-sheets (∼30%) and α-helices (∼24%). Such a stru...
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Surface properties and conformation of Nephila clavipes spider recombinant silk proteins at the air-water interface.
Langmuir, 2009Co-Authors: Anne Renault, Thierry Lefevre, Jean-françois Rioux-dubé, Stéphane Pezennec, Sylvie Beaufils, Véronique Vié, Mélanie Tremblay, Michel PezoletAbstract:The dragline fiber of spiders is composed of two proteins, the major ampullate spidroins I and II (MaSpI and MaSpII). To better understand the assembly mechanism and the properties of these proteins, the adsorption behavior of the recombinant proteins of the spider Nephila clavipes produced by Nexia Biotechnologies Inc. has been studied at the air-water interface using ellipsometry, surface pressure, rheological, and infrared measurements. The results show that the adsorption is more rapid and more molecules are present at the interface for MaSpII than for MaSpI. MaSpII has thus a higher affinity for the interface than MaSpI, which is consistent with its higher aggregation propensity in water. The films formed at the interface consist of networks containing a high content of intermolecular beta-sheets as revealed by the in situ polarization modulation infrared absorption reflection spectra. The infrared results further demonstrate that, for MaSpI, the beta-sheets are formed as soon as the proteins adsorb to the interface while for MaSpII the beta-sheet formation occurs more slowly. The amount of beta-sheets is lower for MaSpII than for MaSpI, most likely due to the presence of proline residues in its sequence. Both proteins form elastic films, but they are heterogeneous for MaSpI and homogeneous for MaSpII most probably as a result of a more ordered and slower aggregation process for MaSpII. This difference in their mechanism of assembly and interfacial behaviors does not seem to arise from their overall hydrophobicity or from a specific pattern of hydrophobicity, but rather from the longer polyalanine motifs, lower glycine content, and higher proline content of MaSpII. The propensity of both spidroins to form beta-sheets, especially the polyalanine blocks, suggests the participation of both proteins in the silk's beta-sheet crystallites.
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conformational and orientational transformation of silk proteins in the major ampullate gland of Nephila clavipes spiders
Biomacromolecules, 2008Co-Authors: Thierry Lefevre, Simon Boudreault, Conrad Cloutier, Michel PezoletAbstract:The orientational and conformational transformation of the native liquid silk into a solid fiber in the major ampullate gland of the spider Nephila clavipes has been studied by Raman spectromicroscopy. The spectra show that the conformation of silk proteins in the glandular sac contains several secondary structure elements, which is consistent with intrinsically unfolded proteins. A few alpha-helices are also present and involve some alanine residues located in the polyalanine segments of the spidroin sequence. The conversion of the silk solution in the major ampullate gland appears to be a two-state process without intermediate states. In the first and second limbs of the duct, silk is isotropic and spidroins are generally native-like. beta-Sheets start to develop between the second and the third limb of the duct, suggesting that early beta-sheets are generated by shear forces. However, most of the beta-sheets are formed between the draw down taper and the valve. The early beta-sheets formed upward of the draw down taper might play the role of nucleation sites for the subsequent beta-sheet aggregation. The alignment of the polypeptides chains occurs near the valve, revealing that orientational and conformational changes do not occur simultaneously. Extensional flow seems to be the driving force to produce the orientational order, which in turn is associated with the formation of the major part of the beta-sheets. The slow evolution of the spidroin conformation up to the draw down taper followed by the rapid transformation between the drawn down taper and the valve may be important to achieve the optimal structure of the final fiber.
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Nephila clavipes spider dragline silk microstructure studied by scanning transmission x ray microscopy
Journal of the American Chemical Society, 2007Co-Authors: Marieeve Rousseau, Daniel Cruz, Marcia M West, And Adam P Hitchcock, Michel PezoletAbstract:Nephila clavipes dragline silk microstructure has been investigated by scanning transmission X-ray microscopy (STXM), a technique that allows quantitative mapping of the level of orientation of the peptide groups at high spatial resolution (<50 nm). Maps of the orientation parameter 〈P2〉 have been derived for spider silk for the first time. Dragline silk presents a very fine microstructure in which small, highly oriented domains (average area of 1800 nm2, thus clearly bigger than individual β-sheet crystallites) are dispersed in a dominant, moderately oriented matrix with several small unoriented domains. Our results also highlight the orientation of the noncrystalline fraction in silk, which has been underestimated in numerous structural models. No evidence of either a regular lamellar structure or any periodicity along the fiber was observed at this spatial resolution. The surface of fresh spider silk sections consists of a ∼30−120 nm thick layer of highly oriented protein chains, which was found to var...
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Nephila clavipes spider dragline silk microstructure studied by scanning transmission x ray microscopy
Journal of the American Chemical Society, 2007Co-Authors: Marieeve Rousseau, Daniel Cruz, Marcia M West, And Adam P Hitchcock, Michel PezoletAbstract:Nephila clavipes dragline silk microstructure has been investigated by scanning transmission X-ray microscopy (STXM), a technique that allows quantitative mapping of the level of orientation of the peptide groups at high spatial resolution (<50 nm). Maps of the orientation parameter P2 have been derived for spider silk for the first time. Dragline silk presents a very fine microstructure in which small, highly oriented domains (average area of 1800 nm2, thus clearly bigger than individual beta-sheet crystallites) are dispersed in a dominant, moderately oriented matrix with several small unoriented domains. Our results also highlight the orientation of the noncrystalline fraction in silk, which has been underestimated in numerous structural models. No evidence of either a regular lamellar structure or any periodicity along the fiber was observed at this spatial resolution. The surface of fresh spider silk sections consists of a approximately 30-120 nm thick layer of highly oriented protein chains, which was found to vary with the reeling speed, where web building (0.5 cm/s) and lifeline (10 cm/s) spinning speeds were investigated. While the average level of orientation of the protein chains is unaffected by the spinning speed, STXM measurements clearly highlight microstructure differences. The slowpull fiber contains a larger fraction of highly oriented domains, while the protein chains are more homogeneously oriented in the fastpull fiber. In comparison, cocoon silk from the silkworm Bombyx mori presents a narrower orientation distribution. The strength-extensibility combination found in spider dragline silk is associated with its broad orientation distribution of highly interdigitated and unoriented domains.
Tetsuo Asakura - One of the best experts on this subject based on the ideXlab platform.
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conformational change of 13c labeled 47 mer model peptides of Nephila clavipes dragline silk in poly vinyl alcohol film by stretching studied by 13c solid state nmr and molecular dynamics simulation
International Journal of Biological Macromolecules, 2019Co-Authors: Tetsuo Asakura, Hironori Matsuda, Akihiro Aoki, Naomi Kataoka, Akiko ImaiAbstract:Abstract For determination of the conformation of irregular sequences in glycine-rich region of the Nephila clavipes spider dragline silk, the combination of 13C selectively labeled model peptides for the typical primary structure and their 13C solid-state NMR observations is very useful (T. Asakura et al. Macromolecules. 51 (2018) 3608–3619). However, spiders produce the fiber through the stretching process in nature and therefore, it is difficult to study conformational change by stretching as mimic using the model peptides because these are generally in the powder form. In this paper, 13C selectively labeled three model peptides, (Glu)4(Ala)6Gly Gly 12 Ala 13 Gly 14 GlnGlyGlyTyrGlyGlyLeuGlySerGln Gly 25 Ala 26 Gly 27 ArgGly-GlyLeuGlyGlyGln Gly 35 Ala 36 Gly 37 (Ala)6(Glu)4 with three underlined 13C labeled blocks and their poly(vinyl alcohol) blend films were prepared and the conformational changes of these peptides were monitored by stretching of the films using 13C solid-state NMR. In addition, the molecular dynamics simulation was done to evaluate change in the conformation of the sequence by stretching theoretically. The fractions of β-sheet of Ala36 and Gly37 residues in glycine-rich region adjacent to the C-terminal (Ala)6 sequence increased significantly by stretching compared with those of other 13C labeled Ala and Gly residues.
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determination of local structure of 13c selectively labeled 47 mer peptides as a model for gly rich region of Nephila clavipes dragline silk using a combination of 13c solid state nmr and md simulation
Macromolecules, 2018Co-Authors: Tetsuo Asakura, Akio Nishimura, Yugo TaseiAbstract:For the first time, we elucidate the complex structure of the Gly-rich regions in Nephila clavipes dragline silk through synergistic experimental and theoretical studies. First, the 13C selectively labeled 47-mer peptides selected from the glycine (Gly)-rich region of N. clavipes dragline silk were synthesized. The 13C CP/MAS NMR spectra were analyzed to determine the fractions of the conformations of individual Gly and Ala residues through 13C conformation-dependent chemical shifts and peak deconvolution. By comparing the 13C solid-state NMR spectra of several simple model peptides, the presence of 31 helix in the 47-mer peptides was disproved, and the (Ala)6 regions were shown to form β-sheet structure in the staggered arrangement. Although the fraction of β-sheet components tended to increase and the fraction of random coil component decrease toward both chain ends, significant change in the fractions was observed depending on the amino acid position. These results were successfully rationalized throug...
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Determination of Local Structure of 13C Selectively Labeled 47-mer Peptides as a Model for Gly-Rich Region of Nephila clavipes Dragline Silk Using a Combination of 13C Solid-State NMR and MD Simulation
2018Co-Authors: Tetsuo Asakura, Akio Nishimura, Yugo TaseiAbstract:For the first time, we elucidate the complex structure of the Gly-rich regions in Nephila clavipes dragline silk through synergistic experimental and theoretical studies. First, the 13C selectively labeled 47-mer peptides selected from the glycine (Gly)-rich region of N. clavipes dragline silk were synthesized. The 13C CP/MAS NMR spectra were analyzed to determine the fractions of the conformations of individual Gly and Ala residues through 13C conformation-dependent chemical shifts and peak deconvolution. By comparing the 13C solid-state NMR spectra of several simple model peptides, the presence of 31 helix in the 47-mer peptides was disproved, and the (Ala)6 regions were shown to form β-sheet structure in the staggered arrangement. Although the fraction of β-sheet components tended to increase and the fraction of random coil component decrease toward both chain ends, significant change in the fractions was observed depending on the amino acid position. These results were successfully rationalized through molecular dynamics simulation
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A two-dimensional spin-diffusion NMR study on the local structure of a water-soluble model peptide for Nephila clavipes dragline silk (MaSp1) before and after spinning
Polymer Journal, 2012Co-Authors: Koji Yazawa, Erika Yamaguchi, Akihiro Aoki, Yasumoto Nakazawa, Yuu Suzuki, Tetsuo AsakuraAbstract:The local structure of the acidic-treated model peptides,(E)_8GGLGGQGAG(A)_6GGAGQGGYGG, derived from the consensus sequence of Nephila clavipes fibroin major ampullate spidroin 1 was determined using two-dimensional proton-driven spin-diffusion solid-state NMR under off-magic-angle spinning coupled with ^13C isotope double labeling of specific residues. We observed a positional dependence on the torsion angles of Ala residues in the β sheet. Torsion angle of the Ala residue at the center of poly-Ala domain concentrates around at ( ϕ , ψ ) = (−150°, 150°), while that of its periphery is distorted and more distributed.
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13C solid-state NMR study of the 13C-labeled peptide, (E)8GGLGGQGAG(A)6GGAGQGGYGG as a model for the local structure of Nephila clavipes dragline silk (MaSp1) before and after spinning †
Biopolymers, 2011Co-Authors: Koji Yazawa, Erika Yamaguchi, David W. Knight, Tetsuo AsakuraAbstract:We prepared the water soluble model peptide, (E)8GGLGGQGAG(A)6GGAGQGGYGG, to throw light on the local structure of spidroin 1 (MaSpl) protein in spider dragline silk of Nephila clavipes before and after spinning. Solution 13C NMR showed that the conformation of the peptide in aqueous solution was essentially random coil. Solid-state NMR was used to follow conformation-dependent 13C chemical shifts in 13C selectively labeled versions of the peptide. The peptide lyophilized from an aqueous solution at neutral pH (hereafter referred to as “without acid treatment)”was used to mimic the state of the spidroin stored in the spider's silk gland while the peptide precipitated from the acidic solution (“with acid treatment”) was used to simulate the role of acid treatment in inducing conformation change in the natural spinning process. In without acid treatment, the fraction of random coil conformation was lowest in the N-terminal region (residues 15–18) when compared with the C-terminus. The conformational change produced by the acid treatment occurred in the sequence, G15AG(A)6GGAG27, interposed between pairs of Gly residues pairs, Gly12,13, and Gly29,30. The acid treated peptide showed a remarkable decrease in the fraction of random coil conformation from A20 to A23 in the poly-Ala region when compared with the peptide without acid treatment. These observations taken together suggest that the peptide can be used as a model for studying the localization of the conformation change in spider silk fibroin in the natural spinning and the role of acid treatment in this process. © 2011 Wiley Periodicals, Inc. Biopolymers 97: 347–354, 2012.
Randolph V Lewis - One of the best experts on this subject based on the ideXlab platform.
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Nephila clavipes flagelliform silk like ggx motifs contribute to extensibility and spacer motifs contribute to strength in synthetic spider silk fibers
Biomacromolecules, 2013Co-Authors: Sherry L Adrianos, Jeffery L Yarger, Florence Teule, Michael B Hinman, Justin A Jones, Warner S Weber, Randolph V LewisAbstract:Flagelliform spider silk is the most extensible silk fiber produced by orb weaver spiders, though not as strong as the dragline silk of the spider. The motifs found in the core of the Nephila clavipes flagelliform Flag protein are GGX, spacer, and GPGGX. Flag does not contain the polyalanine motif known to provide the strength of dragline silk. To investigate the source of flagelliform fiber strength, four recombinant proteins were produced containing variations of the three core motifs of the Nephila clavipes flagelliform Flag protein that produces this type of fiber. The as-spun fibers were processed in 80% aqueous isopropanol using a standardized process for all four fiber types, which produced improved mechanical properties. Mechanical testing of the recombinant proteins determined that the GGX motif contributes extensibility and the spacer motif contributes strength to the recombinant fibers. Recombinant protein fibers containing the spacer motif were stronger than the proteins constructed without the spacer that contained only the GGX motif or the combination of the GGX and GPGGX motifs. The mechanical and structural X-ray diffraction analysis of the recombinant fibers provide data that suggests a functional role of the spacer motif that produces tensile strength, though the spacer motif is not clearly defined structurally. These results indicate that the spacer is likely a primary contributor of strength, with the GGX motif supplying mobility to the protein network of native N. clavipes flagelliform silk fibers.
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quantifying the fraction of glycine and alanine in β sheet and helical conformations in spider dragline silk using solid state nmr
Chemical Communications, 2008Co-Authors: Gregory P Holland, Randolph V Lewis, Janelle E Jenkins, Melinda S Creager, Jeffery L YargerAbstract:Solid-state two-dimensional refocused INADEQUATE MAS NMR experiments resolve distinct helical and β-sheet conformational environments for both alanine and glycine in Nephila clavipes dragline silk fibers; the fraction of alanine and glycine in β-sheet structures is determined to be 82% ± 4% and 28% ± 5%, respectively.
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An investigation of the divergence of major ampullate silk fibers from Nephila clavipes and Argiope aurantia.
Biomacromolecules, 2005Co-Authors: Amanda E. Brooks, Holly B. Steinkraus, Shane R. Nelson, Randolph V LewisAbstract:The major ampullate fiber of both Nephila clavipes and Argiope aurantia is composed of two different proteins, MaSp1 and MaSp2. Each of these proteins has a highly conserved pattern of silk-associated amino acid motifs. The GPGXX motif is the only source of proline and is unique to MaSp2. On the basis of the percent of proline, Nephila clavipes major ampullate silk was calculated to consist of 19% MaSp2 and 81% MaSp1, while Argiope aurantia was calculated to have a significantly higher MaSp2 content of 59% with MaSp1 comprising the remaining 41%. To investigate the functional implications of the difference in protein composition, major ampullate silk fibers from Nephila clavipes and Argiope aurantia were mechanically tested and compared. Stress-strain curves produced from polynomial regression show that the two significant differences between major ampullate silk fibers from Nephila clavipes and Argiope aurantia are the average peak load stress and Young's modulus, with Argiope higher for both.
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hypotheses that correlate the sequence structure and mechanical properties of spider silk proteins
International Journal of Biological Macromolecules, 1999Co-Authors: Cheryl Y. Hayashi, Nichola H Shipley, Randolph V LewisAbstract:Abstract Several types of silks and silk protein coding genes have been characterized from orb-web weaving spiders. When the protein sequences of major ampullate, minor ampullate, and flagelliform silks from Nephila clavipes are compared, they can be summarized as sets of shared amino acid motifs. Four of these motifs and their likely secondary structures are described. Each structural element, termed a module, is then associated with its impact on the mechanical properties of a silk fiber. In particular, correlations are drawn between an alanine-rich ‘crystalline module’ and tensile strength and between a proline-containing ‘elasticity module’ and extensibility.
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conformation of the polyalanine repeats in minor ampullate gland silk of the spider Nephila clavipes
Macromolecules, 1997Co-Authors: Oskar Liivak, Randolph V Lewis, Anthony Flores, Lynn W JelinskiAbstract:Solid state 13C NMR is used to identify the conformation of alanine residues in minor ampullate gland silk from Nephila clavipes and in a genetically engineered protein based on the consensus sequence of MaSp2, a protein present in low concentrations in major ampullate gland silk. The results of the NMR on minor ampullate gland silk are compared to previous NMR data on major ampullate gland silk, and the results on the genetically engineered protein are compared to previous NMR data on the gland fibroin from the major ampullate gland. Differences in the secondary structure of major and minor ampullate gland silk are correlated with mechanical properties. The alanine residues of major ampullate gland silk have previously been shown to consist almost entirely of β-sheet conformations. In contrast, the conformations of the alanine residues of minor ampullate gland silk are more heterogeneous, with a larger fraction of the alanine residues in non-β-sheet conformations. It is hypothesized that these non-β-shee...
Marieeve Rousseau - One of the best experts on this subject based on the ideXlab platform.
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conformation and orientation of proteins in various types of silk fibers produced by Nephila clavipes spiders
Biomacromolecules, 2009Co-Authors: Marieeve Rousseau, Thierry Lefevre, Michel PezoletAbstract:Silk fibers harvested from the web, cocoon, and prey wrapping of the spider Nephila clavipes have been studied by polarized Raman spectromicroscopy. The technique is efficient to differentiate the various types of silk by probing monofilaments produced by the major ampullate (MA), minor ampullate (MI), cylindriform, flagelliform, and aciniform glands. The spectra show that the MA, MI, and cylindriform silks belong to the same structural class and are composed of highly oriented β-sheets (35−37%) with other slightly oriented secondary structures. Spectral markers of particular motifs involved in the β-sheets have been identified. The flagelliform silk represents a second, very peculiar structural class. It displays a heterogeneous disordered conformation without any preferential orientation. Such characteristics certainly play a role in the large extensibility of this silk. The aciniform silk represents a third class of silk dominated by moderately oriented β-sheets (∼30%) and α-helices (∼24%). Such a stru...
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Nephila clavipes spider dragline silk microstructure studied by scanning transmission x ray microscopy
Journal of the American Chemical Society, 2007Co-Authors: Marieeve Rousseau, Daniel Cruz, Marcia M West, And Adam P Hitchcock, Michel PezoletAbstract:Nephila clavipes dragline silk microstructure has been investigated by scanning transmission X-ray microscopy (STXM), a technique that allows quantitative mapping of the level of orientation of the peptide groups at high spatial resolution (<50 nm). Maps of the orientation parameter 〈P2〉 have been derived for spider silk for the first time. Dragline silk presents a very fine microstructure in which small, highly oriented domains (average area of 1800 nm2, thus clearly bigger than individual β-sheet crystallites) are dispersed in a dominant, moderately oriented matrix with several small unoriented domains. Our results also highlight the orientation of the noncrystalline fraction in silk, which has been underestimated in numerous structural models. No evidence of either a regular lamellar structure or any periodicity along the fiber was observed at this spatial resolution. The surface of fresh spider silk sections consists of a ∼30−120 nm thick layer of highly oriented protein chains, which was found to var...
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Nephila clavipes spider dragline silk microstructure studied by scanning transmission x ray microscopy
Journal of the American Chemical Society, 2007Co-Authors: Marieeve Rousseau, Daniel Cruz, Marcia M West, And Adam P Hitchcock, Michel PezoletAbstract:Nephila clavipes dragline silk microstructure has been investigated by scanning transmission X-ray microscopy (STXM), a technique that allows quantitative mapping of the level of orientation of the peptide groups at high spatial resolution (<50 nm). Maps of the orientation parameter P2 have been derived for spider silk for the first time. Dragline silk presents a very fine microstructure in which small, highly oriented domains (average area of 1800 nm2, thus clearly bigger than individual beta-sheet crystallites) are dispersed in a dominant, moderately oriented matrix with several small unoriented domains. Our results also highlight the orientation of the noncrystalline fraction in silk, which has been underestimated in numerous structural models. No evidence of either a regular lamellar structure or any periodicity along the fiber was observed at this spatial resolution. The surface of fresh spider silk sections consists of a approximately 30-120 nm thick layer of highly oriented protein chains, which was found to vary with the reeling speed, where web building (0.5 cm/s) and lifeline (10 cm/s) spinning speeds were investigated. While the average level of orientation of the protein chains is unaffected by the spinning speed, STXM measurements clearly highlight microstructure differences. The slowpull fiber contains a larger fraction of highly oriented domains, while the protein chains are more homogeneously oriented in the fastpull fiber. In comparison, cocoon silk from the silkworm Bombyx mori presents a narrower orientation distribution. The strength-extensibility combination found in spider dragline silk is associated with its broad orientation distribution of highly interdigitated and unoriented domains.