PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “FIBROIN”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed2006

Characterizing the decay of ancient Chinese silk fabrics by microbeam synchrotron radiation diffraction.

Scanning synchrotron radiation microdiffraction with an approximately 1 x 1 microm(2) beam has been used as a novel method for characterizing the decay of several T'ang dynasty (618-907 AD) silk fabrics. The crystalline fraction could be visualized based on beta-sheet 210 reflection intensities, extracted by recursive peak fits from several thousand diffraction patterns recorded during mesh scans. The azimuthal width of the 210 reflection, which is related to the orientation distribution of the crystalline domains within nanofibrils and the macroscopic orientation of the fibers traversed by the beam, was found to be sensitive to the overall state of decay of the fabric. The fine structure of the histogram of azimuthal width was related to the fiber hierarchical microstructure and the fabric morphology. SAXS/WAXS analysis supports the assumption of an initial loss of the random chain network with decay. At a subsequent state of aging, decay proceeds into the nanofibrils and the silk fibers break up into even smaller fractions.

Fibroins↗
PubMed2006

Synthesis and characterization of multiblock copolymers based on spider dragline silk proteins.

Spider dragline silk with its superlative tensile properties provides an ideal system to study the relationship between morphology and mechanical properties of a structural protein. Accordingly, we synthesized two hybrid multiblock copolymers by condensing poly(alanine) [(Ala)(5)] blocks of the structural proteins (spidroin MaSp1 and MaSp2) of spider dragline silk with different oligomers of isoprene (2200 and 5000 Da) having reactive end groups. The synthetic multiblock polymer displayed similar secondary structure to that of natural spidroin, the peptide segment forming a beta-sheet structure. These multiblock polymers showed a significant solubility in the component solvents. Moreover, the copolymer which contains the short polyisoprene segment would aggregate into a micellar-like structure, as observed by TEM.

Animals↗
PubMed2006

Structural analysis of alanine tripeptide with antiparallel and parallel beta-sheet structures in relation to the analysis of mixed beta-sheet structures in Samia cynthia ricini silk protein fiber using solid-state NMR spectroscopy.

The structural analysis of natural protein fibers with mixed parallel and antiparallel beta-sheet structures by solid-state NMR is reported. To obtain NMR parameters that can characterize these beta-sheet structures, (13)C solid-state NMR experiments were performed on two alanine tripeptide samples: one with 100% parallel beta-sheet structure and the other with 100% antiparallel beta-sheet structure. All (13)C resonances of the tripeptides could be assigned by a comparison of the methyl (13)C resonances of Ala(3) with different [3-(13)C]Ala labeling schemes and also by a series of RFDR (radio frequency driven recoupling) spectra observed by changing mixing times. Two (13)C resonances observed for each Ala residue could be assigned to two nonequivalent molecules per unit cell. Differences in the (13)C chemical shifts and (13)C spin-lattice relaxation times (T(1)) were observed between the two beta-sheet structures. Especially, about 3 times longer T(1) values were obtained for parallel beta-sheet structure as compared to those of antiparallel beta-sheet structure, which could be explicable by the difference in the hydrogen-bond networks of both structures. This very large difference in T(1) becomes a good measure to differentiate between parallel or antiparallel beta-sheet structures. These differences in the NMR parameters found for the tripeptides may be applied to assign the parallel and antiparallel beta-sheet (13)C resonances in the asymmetric and broad methyl spectra of [3-(13)C]Ala silk protein fiber of a wild silkworm, Samia cynthia ricini.

Animals↗
PubMed1998

Rotational-echo double-resonance in complex biopolymers: a study of Nephila clavipes dragline silk.

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 provides 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.

Amino Acid Sequence↗
PubMed2002

Controlled release of plasmid DNA from a genetically engineered silk-elastinlike hydrogel.

PURPOSE: The purpose of this study was to evaluate the potential of a genetically engineered silk-elastinlike polymer (SELP) as a matrix for the controlled release of plasmid DNA. METHODS: The influences of SELP concentration, DNA concentration, SELP cure time, and buffer ionic strength on the release of DNA from SELP hydrogels were investigated. To calculate the average effective diffusivity of DNA within the hydrogels, the release data were fitted to a known equation. RESULTS: DNA was released from SELP hydrogels by an ion-exchange mechanism. Under the conditions studied, the release rate was influenced by buffer ionic strength, SELP concentration, and SELP cure time but not DNA concentration. The apparent diffusivity of pRL-CMV plasmid DNA in SELP hydrogels ranged from 3.78 +/- 0.37 x 10(-10) cm2/s (for hydrogels containing 12% w/w SELP and cured for 4 h) to 4.69 +/- 2.81 x 10(-9) cm2/s (for hydrogels containing 8% w/w SELP and cured for 1 h). CONCLUSIONS: The ability to precisely customize the structure and physicochemical properties of SELPs using recombinant techniques, coupled with their ability to form injectable, in situ hydrogel depots that release DNA, renders this class of polymers an interesting candidate for further evaluation in controlled gene delivery.

Amino Acid Sequence↗
PubMed2005

Differential polymerization of the two main protein components of dragline silk during fibre spinning.

Spider silks are some of the strongest materials found in nature. Achieving the high tensile strength and elasticity of the dragline of orb-weaving spiders, such as Nephila clavipes, is a principal goal in biomimetics research. The dragline has a composite nature and is predominantly made up by two proteins, the major ampullate spidroins 1 and 2 (refs 3, 6, 7), which can be considered natural block copolymers. On the basis of their molecular structures both spidroins are thought to contribute, in different ways, to the mechanical properties of dragline silk. The spinning process itself is also considered important for determining the observed features by shaping the hierarchical structure of the fibre. Here we study the heterogeneous distribution of proteins along the radial axis of the fibre. This heterogeneity is generated during the conversion of the liquid spinning dope into solid fibre. Whereas spidroin 1 is distributed almost uniformly within the fibre core, spidroin 2 is missing in the periphery and is tightly packed in certain core areas. Our findings suggest that the role of spidroin 2 in the spinning process could be to facilitate the formation of fibrils and contribute directly to the elasticity of the silk.

Crystallization↗
PubMed2005

Relationships between supercontraction and mechanical properties of spider silk.

Typical spider dragline silk tends to outperform other natural fibres and most man-made filaments. However, even small changes in spinning conditions can have large effects on the mechanical properties of a silk fibre as well as on its water uptake. Absorbed water leads to significant shrinkage in an unrestrained dragline fibre and reversibly converts the material into a rubber. This process is known as supercontraction and may be a functional adaptation for the silk's role in the spider's web. Supercontraction is thought to be controlled by specific motifs in the silk proteins and to be induced by the entropy-driven recoiling of molecular chains. In analogy, in man-made fibres thermal shrinkage induces changes in mechanical properties attributable to the entropy-driven disorientation of 'unfrozen' molecular chains (as in polyethylene terephthalate) or the 'broken' intermolecular hydrogen bonds (as in nylons). Here we show for Nephila major-ampullate silk how in a biological fibre the spinning conditions affect the interplay between shrinkage and mechanical characteristics. This interaction reveals design principles linking the exceptional properties of silk to its molecular orientation.

Animals↗
PubMed2002

Amyloidogenic nature of spider silk.

In spiders soluble proteins are converted to form insoluble silk fibres, stronger than steel. The final fibre product has long been the subject of study; however, little is known about the conversion process in the silk-producing gland of the spider. Here we describe a study of the conversion of the soluble form of the major spider-silk protein, spidroin, directly extracted from the silk gland, to a beta-sheet enriched state using circular dichroism (CD) spectroscopy. Combined with electron microscopy (EM) data showing fibril formation in the beta-sheet rich region of the gland and amino-acid sequence analyses linking spidroin and amyloids, these results lead us to suggest that the refolding conversion is amyloid like. We also propose that spider silk could be a valuable model system for testing hypotheses concerning beta-sheet formation in other fibrilogenic systems, including amyloids.

Amino Acid Sequence↗
PubMed2006

Novel nanocomposites from spider silk-silica fusion (chimeric) proteins.

Silica skeletal architectures in diatoms are characterized by remarkable morphological and nanostructural details. Silk proteins from spiders and silkworms form strong and intricate self-assembling fibrous biomaterials in nature. We combined the features of silk with biosilica through the design, synthesis, and characterization of a novel family of chimeric proteins for subsequent use in model materials forming reactions. The domains from the major ampullate spidroin 1 (MaSp1) protein of Nephila clavipes spider dragline silk provide control over structural and morphological details because it can be self-assembled through diverse processing methods including film casting and fiber electrospinning. Biosilica nanostructures in diatoms are formed in aqueous ambient conditions at neutral pH and low temperatures. The R5 peptide derived from the silaffin protein of Cylindrotheca fusiformis induces and regulates silica precipitation in the chimeric protein designs under similar ambient conditions. Whereas mineralization reactions performed in the presence of R5 peptide alone form silica particles with a size distribution of 0.5-10 microm in diameter, reactions performed in the presence of the new fusion proteins generate nanocomposite materials containing silica particles with a narrower size distribution of 0.5-2 microm in diameter. Furthermore, we demonstrate that composite morphology and structure could be regulated by controlling processing conditions to produce films and fibers. These results suggest that the chimeric protein provides new options for processing and control over silica particle sizes, important benefits for biomedical and specialty materials, particularly in light of the all aqueous processing and the nanocomposite features of these new materials.

Amino Acid Sequence↗
PubMed2002

Segmented nanofibers of spider dragline silk: atomic force microscopy and single-molecule force spectroscopy.

Despite its remarkable materials properties, the structure of spider dragline silk has remained unsolved. Results from two probe microscopy techniques provide new insights into the structure of spider dragline silk. A soluble synthetic protein from dragline silk spontaneously forms nanofibers, as observed by atomic force microscopy. These nanofibers have a segmented substructure. The segment length and amino acid sequence are consistent with a slab-like shape for individual silk protein molecules. The height and width of nanofiber segments suggest a stacking pattern of slab-like molecules in each nanofiber segment. This stacking pattern produces nano-crystals in an amorphous matrix, as observed previously by NMR and x-ray diffraction of spider dragline silk. The possible importance of nanofiber formation to native silk production is discussed. Force spectra for single molecules of the silk protein demonstrate that this protein unfolds through a number of rupture events, indicating a modular substructure within single silk protein molecules. A minimal unfolding module size is estimated to be around 14 nm, which corresponds to the extended length of a single repeated module, 38 amino acids long. The structure of this spider silk protein is distinctly different from the structures of other proteins that have been analyzed by single-molecule force spectroscopy, and the force spectra show correspondingly novel features.

Amino Acid Sequence↗
PubMed2002

The molecular structure of spider dragline silk: folding and orientation of the protein backbone.

The design principles of spider dragline silk, nature's high-performance fiber, are still largely unknown, in particular for the noncrystalline glycine-rich domains, which form the bulk of the material. Here we apply two-dimensional solid-state NMR to determine the distribution of the backbone torsion angles (phi,psi) as well as the orientation of the polypeptide backbone toward the fiber at both the glycine and alanine residues. Instead of an "amorphous matrix," suggested earlier for the glycine-rich domains, these new data indicate that all domains in dragline silk have a preferred secondary structure and are strongly oriented, with the chains predominantly parallel to the fiber. As proposed previously, the alanine residues are predominantly found in a beta sheet conformation. The glycine residues are partly incorporated into the beta sheets and otherwise form helical structures with an approximate 3-fold symmetry.

Animals↗
PubMed1968

Studies on the posterior silk gland of the silkworm, Bombyx mori. II. Cytolytic processes in posterior silk gland cells during metamorphosis from larva to pupa.

Cytolytic processes in posterior silk gland cells of the silkworm, Bombyx mori, during metamorphosis from larva to pupa have been studied. During this stage, the wet weight and the amounts of RNA and protein of the gland decrease rapidly and markedly, while the amount of DNA decreases slowly and slightly. The ultrastructural changes observed at the beginning of the prepupal stage consist of the appearance or the increase in the number of autophagosomes containing endoplasmic reticulum (ER), or "early autophagosomes" as we have called them, which seem to be gradually transformed to autolysosomes. A number of usual lysosomes, which frequently contain myelin figures, also appear in the cytoplasm. Sometimes they fuse with each other to form large conglomerates. In the middle of the prepupal stage, a number of smooth membrane-bounded vacuoles appear in cytoplasm. Towards the end of the prepupal stage the partition or sequestration of cytoplasm was observed. Thus large autophagosomes containing cytoplasmic organelles such as rough ER and/or mitochondria are formed. The nucleus is partitioned in a similar way by smooth membranes, and then autophagosomes containing condensed chromatin blocks are formed. These various kinds of autophagosomes, or "late autophagosomes" as we have generally called them, are continuously released into the hemolymph until the gland is completely disintegrated.

Animals↗