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Asakura T, Williamson MP. A review on the structure of Bombyx mori silk fibroin fiber studied using solid-state NMR: An antipolar lamella with an 8-residue repeat. Int J Biol Macromol 2023:125537. [PMID: 37379946 DOI: 10.1016/j.ijbiomac.2023.125537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 06/19/2023] [Accepted: 06/21/2023] [Indexed: 06/30/2023]
Abstract
Silk fibroin (SF) fiber from the silkworm Bombyx mori in the Silk II form has been used as an excellent textile fiber for over 5000 years. Recently it has been developed for a range of biomedical applications. Further expansion of these uses builds on the excellent mechanical strength of SF fiber, which derives from its structure. This relationship between strength and SF structure has been studied for over 50 years, but it is still not well understood. In this review, we report the use of solid-state NMR to study stable-isotope labeled SF fiber and stable-isotope labeled peptides including (Ala-Gly)15 and (Ala-Gly-Ser-Gly-Ala-Gly)5 as models of the crystalline fraction. We show that the crystalline fraction is a lamellar structure with a repetitive folding using β-turns every eighth amino acid, and that the sidechains adopt an antipolar arrangement rather than the more well-known polar structure described by Marsh, Corey and Pauling (that is, the Ala methyls in each layer point in opposite directions in alternate strands). The amino acids Ser, Tyr and Val are the next most common in B. mori SF after Gly and Ala, and occur in the crystalline and semi-crystalline regions, probably defining the edges of the crystalline region. Thus, we now have an understanding of the main features of Silk II but there is still a long way to go.
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Affiliation(s)
- Tetsuo Asakura
- Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan.
| | - Mike P Williamson
- School of Biosciences, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
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Lei F, Cai J, Lyu R, Shen H, Xu Y, Wang J, Shuai Y, Xu Z, Mao C, Yang M. Efficient Tumor Immunotherapy through a Single Injection of Injectable Antigen/Adjuvant-Loaded Macroporous Silk Fibroin Microspheres. ACS Appl Mater Interfaces 2022; 14:42950-42962. [PMID: 36112417 DOI: 10.1021/acsami.2c11286] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Synthetic or natural materials have been used as vaccines in cancer immunotherapy. However, using them as vaccines necessitates multiple injections or surgical implantations. To tackle such daunting challenges, we develop an injectable macroporous Bombyx mori (B. mori) silk fibroin (SF) microsphere loaded with antigens and immune adjuvants to suppress established tumors with only a single injection. SF microspheres can serve as a scaffold by injection and avoid surgical injury as seen in traditional scaffold vaccines. The macroporous structure of the vaccine facilitates the recruitment of immune cells and promotes the activation of dendritic cells (DCs), resulting in a favorable immune microenvironment that further induces strong humoral and cellular immunity. We have also modified the vaccine into a booster version by simply allowing the antigens to be adsorbed onto the SF microspheres. The booster vaccine highly efficiently suppresses tumor growth by improving the cytotoxic T lymphocyte (CTL) response. In general, these results demonstrate that the macroporous SF microspheres can serve as a facile platform for tumor vaccine therapy in the future. Since the SF microspheres are also potential scaffolds for tissue regeneration, their use as a vaccine platform will enable their applications in eradicating tumors while regenerating healthy tissue to heal the tumor-site cavity.
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Affiliation(s)
- Fang Lei
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Jiangfeng Cai
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Ruyin Lyu
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Honglan Shen
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Yalan Xu
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Jie Wang
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Yajun Shuai
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Zongpu Xu
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
| | - Chuanbin Mao
- School of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, P.R. China
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United States
| | - Mingying Yang
- Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P.R. China
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Asakura T. Structure of Silk I ( Bombyx mori Silk Fibroin before Spinning) -Type II β-Turn, Not α-Helix. Molecules 2021; 26:3706. [PMID: 34204550 DOI: 10.3390/molecules26123706] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Revised: 06/11/2021] [Accepted: 06/14/2021] [Indexed: 12/04/2022] Open
Abstract
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. In conclusion, the author emphasized here that silk I structure should be type II β-turn, not α-helix.
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Asakura T, Ogawa T, Naito A, Williamson MP. Chain-folded lamellar structure and dynamics of the crystalline fraction of Bombyx mori silk fibroin and of (Ala-Gly-Ser-Gly-Ala-Gly) n model peptides. Int J Biol Macromol 2020; 164:3974-3983. [PMID: 32882279 DOI: 10.1016/j.ijbiomac.2020.08.220] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 08/27/2020] [Accepted: 08/28/2020] [Indexed: 02/08/2023]
Abstract
Solid-state NMR is a powerful analytical technique to determine the composite structure of Bombyx mori silk fibroin (SF). In our previous paper, we proposed a lamellar structure for Ala-Gly copolypeptides as a model of the crystalline fraction in Silk II. In this paper, the structure and dynamics of the crystalline fraction and of a better mimic of the crystalline fraction, (Ala-Gly-Ser-Gly-Ala-Gly)n (n = 2-5, 8), and 13C selectively labeled [3-13C]Ala-(AGSGAG)5 in Silk II forms, were studied using structural and dynamical analyses of the Ala Cβ peaks in 13C cross polarization/ magic angle spinning NMR and 13C solid-state spin-lattice relaxation time (T1) measurements, respectively. Like Ala-Gly copolypeptides, these materials have lamellar structures with two kinds of Ala residues in β-sheet, A and B, plus one distorted β-turn, t, formed by repetitive folding using β-turns every eighth amino acid in an antipolar arrangement. However, because of the presence of Ser residues at every sixth residue in (AGSGAG)n, the T1 values and mobilities of B decreased significantly. We conclude that the Ser hydroxyls hydrogen bond to adjacent lamellar layers and fix them together in a similar way to Velcro®.
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Affiliation(s)
- Tetsuo Asakura
- Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
| | - Tatsuya Ogawa
- Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
| | - Akira Naito
- Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
| | - Michael P Williamson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
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Zhang X, Liang J, Chen Z, Donley C, Liu Y, Cheng G. Chemical modification of Bombyx mori silk fibers with vinyl groups for thiol-ene click chemistry. BMC Chem 2019; 13:114. [PMID: 31517313 PMCID: PMC6734490 DOI: 10.1186/s13065-019-0630-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2019] [Accepted: 08/31/2019] [Indexed: 11/10/2022] Open
Abstract
Natural Bombyx mori silk fibroin (SF) fibers were modified with 2-methacryloyloxyethyl isocyanate (MOI) first for the introduction of vinyl groups. Then, 1H,1H,2H,2H-perfluorodecanethiol was grafted onto the SF fibers via thiol-ene click chemistry using ultraviolet light. The formations of MOI-modified and PFDT-grafted SF fibers were analyzed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The morphology of samples was also revealed by a scanning electron microscope. In addition, differential scanning calorimetry results demonstrated that SF fibers did not show significant change in thermal behavior, regardless of the chemical modification. To confirm the cytotoxicity of the prepared SF fibers, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay was performed, and no toxicity was observed with PFDT-grafted SF fibers. The results also showed that PFDT-grafted SF fibers exhibited good antifouling properties when Chlorella vulgaris (C. vulgaris) was selected as a model for algal cells adhesion experiment.
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Affiliation(s)
- Xiaoning Zhang
- 1State Key Laboratory of Silkworm Genome Biology, College of Biotechnology, Southwest University, Chongqing, 400715 China
| | - Jianwei Liang
- 1State Key Laboratory of Silkworm Genome Biology, College of Biotechnology, Southwest University, Chongqing, 400715 China
| | - Zhenyu Chen
- 1State Key Laboratory of Silkworm Genome Biology, College of Biotechnology, Southwest University, Chongqing, 400715 China
| | - Carrie Donley
- 2Chapel Hill Analytical and Nanofabrication Laboratory, Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3216 USA
| | - Yuling Liu
- 1State Key Laboratory of Silkworm Genome Biology, College of Biotechnology, Southwest University, Chongqing, 400715 China
| | - Guotao Cheng
- 1State Key Laboratory of Silkworm Genome Biology, College of Biotechnology, Southwest University, Chongqing, 400715 China
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Abstract
As the incidences of cardiovascular diseases have been on the rise in recent years, the need for small-diameter artificial vascular grafts is increasing globally. Although synthetic polymers such as expanded polytetrafluoroethylene or poly(ethylene terephthalate) have been successfully used for artificial vascular grafts ≥6 mm in diameter, they fail at smaller diameters (<6 mm) due to thrombus formation and intimal hyperplasia. Thus, development of vascular grafts for small diameter vessel replacement that are <6 mm in diameter remains a major clinical challenge. Silk fibroin (SF) from Bombyx mori silkworm is well-known as an excellent textile and also has been used as suture material in surgery for more than 2000 years. Many attempts to develop small-diameter SF vascular grafts with <6 mm in diameter have been reported. Here, research and development in small-diameter vascular grafts with SF are reviewed as follows: (1) the heterogeneous structure of SF fiber (Silk II), including the packing arrangements and type II β-turn structure of SF (Silk I*) before spinning; (2) SF modified by transgenic silkworm, which is more suitable for vascular grafts; (3) preparation of small-diameter SF vascular grafts; (4) characterization of SF in the hydrated state, including dynamics of water molecules by nuclear magnetic resonance; and (5) evaluation of the SF grafts by in vivo implantation experiment. According to the findings, SF is a promising material for small-diameter vascular graft development.
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Affiliation(s)
- Tetsuo Asakura
- Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
| | - Takashi Tanaka
- Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
| | - Ryo Tanaka
- Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
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Asakura T, Isobe K, Kametani S, Ukpebor OT, Silverstein MC, Boutis GS. Characterization of water in hydrated Bombyx mori silk fibroin fiber and films by 2H NMR relaxation and 13C solid state NMR. Acta Biomater 2017; 50:322-333. [PMID: 28065870 DOI: 10.1016/j.actbio.2016.12.052] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2016] [Revised: 11/30/2016] [Accepted: 12/29/2016] [Indexed: 11/18/2022]
Abstract
The mechanical properties of Bombyx mori silk fibroin (SF), such as elasticity and tensile strength, change remarkably upon hydration. However, the microscopic interaction with water is not currently well understood on a molecular level. In this work, the dynamics of water molecules interacting with SF was studied by 2H solution NMR relaxation and exchange measurements. Additionally, the conformations of hydrated [3-13C]Ala-, [3-13C]Ser-, and [3-13C]Tyr-SF fibers and films were investigated by 13C DD/MAS NMR. Using an inverse Laplace transform algorithm, we were able to identify four distinct components in the relaxation times for water in SF fiber. Namely, A: bulk water outside the fiber, B: water molecules trapped weakly on the surface of the fiber, C: bound water molecules located in the inner surface of the fiber, and D: bound water molecules located in the inner part of the fiber were distinguishable. In addition, four components were also observed for water in the SF film immersed in methanol for 30s, while only two components for the film immersed in methanol for 24h. The effects of hydration on the conformation of Ser and Tyr residues in the site-specific crystalline and non-crystalline domains of 13C selectively labeled SF, respectively, could be determined independently. Our measurements provide new insight relating the characteristics of water and the hydration structure of silk, which are relevant in light of current interest in the design of novel silk-based biomaterials. STATEMENTS OF SIGNIFICANCE The mechanical properties of Bombyx mori silk fibroin (SF) change remarkably upon hydration. However, the microscopic interaction between SF and water is not currently well understood on a molecular level. We were able to identify four distinct components in the relaxation times for water in SF fiber by 2H solution NMR relaxation and exchange measurements. In addition, the effects of hydration on the conformation of Ser and Tyr residues in the site-specific crystalline and non-crystalline domains of 13C selectively labeled SF, respectively, could be determined independently. Thus, our measurements provide new insight relating the characteristics of water and the hydration structure of silk, which are relevant in light of current interest in the design of novel silk-based biomaterials.
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Affiliation(s)
- Tetsuo Asakura
- Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
| | - Kotaro Isobe
- Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
| | - Shunsuke Kametani
- Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
| | - Obehi T Ukpebor
- Department of Physics, Hunter College of The City University of New York, 695 Park Avenue, NY 10065, USA
| | - Moshe C Silverstein
- Department of Physics, Hunter College of The City University of New York, 695 Park Avenue, NY 10065, USA
| | - Gregory S Boutis
- Department of Physics, Brooklyn College of The City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA; Department of Physics, The Graduate Center of The City University of New York, 365 5th Avenue, New York, NY 10016, USA.
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Suzuki S, Dawson RA, Chirila TV, Shadforth AMA, Hogerheyde TA, Edwards GA, Harkin DG. Treatment of Silk Fibroin with Poly(ethylene glycol) for the Enhancement of Corneal Epithelial Cell Growth. J Funct Biomater 2015; 6:345-66. [PMID: 26034883 PMCID: PMC4493516 DOI: 10.3390/jfb6020345] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 05/26/2015] [Accepted: 05/26/2015] [Indexed: 12/14/2022] Open
Abstract
A silk protein, fibroin, was isolated from the cocoons of the domesticated silkworm (Bombyx mori) and cast into membranes to serve as freestanding templates for tissue-engineered corneal cell constructs to be used in ocular surface reconstruction. In this study, we sought to enhance the attachment and proliferation of corneal epithelial cells by increasing the permeability of the fibroin membranes and the topographic roughness of their surface. By mixing the fibroin solution with poly(ethylene glycol) (PEG) of molecular weight 300 Da, membranes were produced with increased permeability and with topographic patterns generated on their surface. In order to enhance their mechanical stability, some PEG-treated membranes were also crosslinked with genipin. The resulting membranes were thoroughly characterized and compared to the non-treated membranes. The PEG-treated membranes were similar in tensile strength to the non-treated ones, but their elastic modulus was higher and elongation lower, indicating enhanced rigidity. The crosslinking with genipin did not induce a significant improvement in mechanical properties. In cultures of a human-derived corneal epithelial cell line (HCE-T), the PEG treatment of the substratum did not improve the attachment of cells and it enhanced only slightly the cell proliferation in the longer term. Likewise, primary cultures of human limbal epithelial cells grew equally well on both non-treated and PEG-treated membranes, and the stratification of cultures was consistently improved in the presence of an underlying culture of irradiated 3T3 feeder cells, irrespectively of PEG-treatment. Nevertheless, the cultures grown on the PEG-treated membranes in the presence of feeder cells did display a higher nuclear-to-cytoplasmic ratio suggesting a more proliferative phenotype. We concluded that while the treatment with PEG had a significant effect on some structural properties of the B. mori silk fibroin (BMSF) membranes, there were minimal gains in the performance of these materials as a substratum for corneal epithelial cell growth. The reduced mechanical stability of freestanding PEG-treated membranes makes them a less viable choice than the non-treated membranes.
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Affiliation(s)
- Shuko Suzuki
- Queensland Eye Institute, South Brisbane, Queensland 4101, Australia.
| | - Rebecca A Dawson
- Queensland Eye Institute, South Brisbane, Queensland 4101, Australia.
- School of Biomedical Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Queensland 4001, Australia.
| | - Traian V Chirila
- Queensland Eye Institute, South Brisbane, Queensland 4101, Australia.
- Science and Engineering Faculty, Queensland University of Technology, Brisbane, Queensland 4001, Australia.
- Faculty of Medicine and Biomedical Sciences, University of Queensland, Herston, Queensland 4029, Australia.
- Australian Institute for Bioengineering and Nanotechnology, University of Queensland, St Lucia, Queensland 4072, Australia.
- Faculty of Science, University of Western Australia, Crawley, Western Australia 6009, Australia.
| | - Audra M A Shadforth
- Queensland Eye Institute, South Brisbane, Queensland 4101, Australia.
- School of Biomedical Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Queensland 4001, Australia.
| | - Thomas A Hogerheyde
- Queensland Eye Institute, South Brisbane, Queensland 4101, Australia.
- School of Biomedical Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Queensland 4001, Australia.
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Queensland 4059, Australia.
| | - Grant A Edwards
- Australian Institute for Bioengineering and Nanotechnology, University of Queensland, St Lucia, Queensland 4072, Australia.
| | - Damien G Harkin
- Queensland Eye Institute, South Brisbane, Queensland 4101, Australia.
- School of Biomedical Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Queensland 4001, Australia.
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Queensland 4059, Australia.
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