Twisted single crystals of Bombyx mori silk fibroin and related model polypeptides with β structure

Lotz, Bernard; Gonthier-Vassal, A.; Brack, Andrè; Magoshi, Jun

doi:10.1016/0022-2836(82)90333-3

Cited by 87 publications

(81 citation statements)

References 32 publications

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“…[61] Lotz et al used transmission electron microscopy to investigate twisted crystals from the chymotrypsin precipitate fraction of B. mori silkworm silk. [62] In this study, the crystallinity levels can be explained using this model from the perspective of the strength of hydrogen bonds involved in b-sheet formation. When the number of polyalanine blocks was increased in the samples (i.e., the length of polyalanine segment was increased), this promote the formation of the stacks of b-pleated sheets.…”

Section: Resultsmentioning

confidence: 99%

Role of Polyalanine Domains in β‐Sheet Formation in Spider Silk Block Copolymers

Rabotyagova

Cebe

Kaplan

2009

Macromolecular Bioscience

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Genetically engineered spider silk-like block copolymers were studied to determine the influence of polyalanine domain size on secondary structure. The role of polyalanine block distribution on beta-sheet formation was explored using FT-IR and WAXS. The number of polyalanine blocks had a direct effect on the formation of crystalline beta-sheets, reflected in the change in crystallinity index as the blocks of polyalanines increased. WAXS analysis confirmed the crystalline nature of the sample with the largest number of polyalanine blocks. This approach provides a platform for further exploration of the role of specific amino acid chemistries in regulating the assembly of beta-sheet secondary structures, leading to options to regulate material properties through manipulation of this key component in spider silks.

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Section: Resultsmentioning

confidence: 99%

Role of Polyalanine Domains in β‐Sheet Formation in Spider Silk Block Copolymers

Rabotyagova

Cebe

Kaplan

2009

Macromolecular Bioscience

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“…It is unlikely that such short chains can serve as a model for the twist of a 83-sheet because of the large influence of the end groups (1). In addition, as pointed out by Lotz et al (21), "the validity [of the calculations in ref. 20] might be questioned, since not even linear, but actually colinear NH-OC hydrogen bonds have been considered, which is a situation seldom encountered in practice.…”

Section: Resultsmentioning

confidence: 99%

Origin of the right-handed twist of beta-sheets of poly(LVal) chains.

Chou¹,

Scheraga²

1982

Proc. Natl. Acad. Sci. U.S.A.

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The energies of three-and five-chain antiparallel and parallel .8-sheets were minimized. Each chain consisted of Six L-valine residues with CH3CO and NHCH3 end groups; the chains were considered to be equivalent, but all dihedral angles of a given chain were allowed to vary independently during energy minimization. The minimum-energy structures had a considerable right-handed twist, as observed in globular proteins. This righthanded twist is due primarily to intrachain nonbonded interactions. Such interactions between the Ct'H3 group of the ith residue and the Cy2H3 group of the (i+2)th residue of the same chain favor a twist of either handedness over the flat structure. However, many small intrastrand pair-wise interatomic interactions involving the CY1H3 and Cy2H3 groups, especially the interactions of these groups with the 0 and amide H atoms of the neighboring peptide groups, make the right-handed twisted structure energetically more favorable than the left-handed one. The intrastrand side-chain torsional energy plays a small additional role in favoring the right-twisted structure over both the flat and the left-twisted structures. The interstrand interactions favor flat structures, but they are not strong enough to overcome the intrastrand interactions that favor the twisted structure; they only decrease somewhat the extent of the right-handed twist of the fl-sheets.We recently showed that minimum-energy structures of 1-sheets consisting of poly(LAla) chains have a right-handed twist addition to the earlier-demonstrated role of the backbone) in producing the right-handed twist. COMPUTATIONAL METHODSComputations were carried out on a single polypeptide chain and on parallel and antiparallel three-and five-stranded 13-sheets. Each chain had the composition CH3CO-(L-Val)6-NHCH3. The residue geometry and energy parameters were those of the ECEPP algorithm [empirical conformational energy program for peptides (6)] (see ref. 1 for further computational details).Generation of 13-Sheets. For a 13-sheet with equivalent strands, the first chain can be generated by using the ECEPP algorithm, and then all the other chains can be generated by iterative rotational and translational operations on the preceding chain; i.e., the ith chain can be generated from the (i-l)th chain by the following equation:where ri and ri-1 are the coordinates of corresponding atoms in the ith and (i-l)th chains, respectively, T = (t1,t2,t3) is a translational vector, and Qi is the following Euler rotational operator (1), as observed in globular proteins (2). As in the case of righthanded a-helices (3), it is the intrastrand nonbonded interaction energy that plays the key role in forcing 13-sheets of L-amino acids to adopt a right-handed twist. The nonbonded energy contribution favoring the right-handed twist is the result of many small intrastrand pair-wise interatomic interactions involving the CPH3 groups; interstrand nonbonded interactions, also involving the C"H3 groups, contribute somewhat, but less so, in influencing the twist....

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“…In right-handed helical lamellar crystals, the molecular chain orientation is double twisted (morphological chirality: the tertiary structure). This double-twist packing is similar to a stack of twisted b-sheets similar to several biopolymers [8][9][10][11]. The twisted sheets pack closely with a twist that is perpendicular to the helical axis of the sheets them- as an example [8].…”

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confidence: 95%

Double Twist in Helical Polymer “Soft” Crystals

Cheng

et al. 1999

Phys. Rev. Lett.

124

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In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions. In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first time a double-twist molecular orientation in a helical crystal has been observed.PACS numbers: 61.41. + e Biological materials and their fascinating functions in the human genome have been extensively explored and continue to stimulate new research directions in materials science. Synthetic polymers are similar to proteins and deoxyribonucleic acids (DNA) with respect to their long chain nature, but synthesizing polymers which possess properties similar to biomaterials require, at the very least, an introduction of chirality. The chirality effect on the material properties and structures of small molecular liquid crystals indicates that a series of new phases exist through the introduction of chiral centers which have interesting electro-optical behaviors [1][2][3][4][5]. A helical morphology with a pitch length of several micrometers is typical of chiral liquid crystalline (LC) phases, but exists only in low ordered LC phases. In highly ordered smectic crystal phases, the helical morphology is suppressed by the crystallization process, leading to the traditional parallel close packing scheme in three-dimensional space [1]. We expect that by directionally connecting small LC molecules with covalent bonds to form main-chain nonracemic chiral LC polymers will lead to an enhancement of the conformational chirality strength. The chirality strength should be strong enough to compete with the parallel close packing scheme during crystallization and stabilize the helical morphology in a crystalline state.The material studied is a main-chain chiral polyester synthesized from ͑R͒-͑2͒-4 0 -͕v-͓2-͑ p-hydroxy-o-nitrophenyloxy͒-1-propyloxy͔-1-nonyloxy͖-4-biphenyl carboxylic acid. The polymer has a spacer of nine methylene units, and is abbreviated as PET͑R ‫ء‬ ͒-9, This polymer was specifically synthesized by an A-B type of condensation to ensure strict head-to-tail connections between adjacent repeating units [6,7]. The polymer possesses right-handed chiral centers ‫͒ء͑‬ along the mainchain backbone. The specific rotation of the monomer is 228.5 ± . The molecular weight of PET͑R ‫ء‬ ͒-9 is approximately 16 000 g͞mol with a polydispersity of 2 after fractionation, as measured by gel permeation chromatography based on polystyrene standards.Polymer thin films (approximate thickness of 50-100 nm) were prepared by casting a 0.05 (wt) % te...

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Twisted single crystals of Bombyx mori silk fibroin and related model polypeptides with β structure

Cited by 87 publications

References 32 publications

Role of Polyalanine Domains in β‐Sheet Formation in Spider Silk Block Copolymers

Role of Polyalanine Domains in β‐Sheet Formation in Spider Silk Block Copolymers

Origin of the right-handed twist of beta-sheets of poly(LVal) chains.

Double Twist in Helical Polymer “Soft” Crystals

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