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At least 19 recordsLinked to original sources
PubMed1976

Studies on silk secretion in the Trichoptera (F. Limmephilidae). II. Structure and amino acid composition of the silk.

The ultrastructure and amino acid composition of the secreted silk of two species of trichopteran larvae, Pycnopsyche guttifer (Walk.) and Neophylax concinnus McL., were investigated. The spinnerets of these two animals were also examined by scanning electron microscopy. The silk consists of double-stranded, flat ribbons (1-4 mu wide), composed of bundles of 15-25 A filaments. There are two components of the silk: the fiber proper and a surrounding coat thought to be a silk "gum". Only the outer coat is positive to the EM PATP technique of Thiery (1967), which indicated the presence of neutral sugars. Amino acid analyses of Pycnopsyche silk show that, like other silks, two predominant amino acids are glycine and serine. Arginine, unexpectedly, is the third most abundant and there are a large number of basic and long side-chain amino acids. X-ray diffraction studies of the silk indicate that it has a less crystalline, more amorphous structure than that of other silks.

Amino Acids↗
PubMed1992

Isolation of a clone encoding a second dragline silk fibroin. Nephila clavipes dragline silk is a two-protein fiber.

Spider dragline silk is a unique protein fiber possessing both high tensile strength and high elasticity. A partial cDNA clone for one dragline silk protein (Spidroin 1) was previously isolated. However, the predicted amino acid sequence could not account for the amino acid composition of dragline silk. We have isolated a partial cDNA clone for another dragline silk protein (Spidroin 2), demonstrating that dragline silk is composed of multiple proteins. The amino acid sequence exhibits an entirely different repetitive motif than Spidroin 1. Spidroin 2 is predicted to consist of linked beta-turns in proline-rich regions which alternate with beta-sheet regions composed of polyalanine segments. This structure for Spidroin 2 provides a model for dragline silk structure and function.

Amino Acid Sequence↗
PubMed1975

The biosynthesis of transfer RNA in insects. I. Increase of amino acid acceptor activity of specific tRNA's utilized for silk protein biosynthesis in the silk gland of Bombyx mori.

1) To detect the quantitative changes of amino acid acceptor activity of tRNA's from the posterior and middle silk glands of Bombyx mori at various ages, a relatively simple and rapid method was established using a mixture of radioactive amino acids in Chlorella hydrolysate. 2) The acceptor activities of silk gland tRNA for 15 amino acids tested seemed to be almost on the same level at the end of the 4th moult stage. During the 5th instar, however, characteristic increases were observed in glycine, alanine, and serine acceptor activities in both silk glands. 3) In the posterior silk gland, which produces fibroin, the acceptor activities for glycine and alanine increased more than that for serine. In the middle silk gland, which produces sericine, the acceptor activity for serine increased more than those for glycine and alanine. 4) In the light of observations on the increase of corresponding aminoacyl-tRNA synthetase activities in the silk glands, a functional adaptation of tRNA synthesis in the tissue is discussed.

Alanine-tRNA Ligase↗
PubMed1979

Discontinuous translation of silk fibroin in a reticulocyte cell-free system and in intact silk gland cells.

Silk fibroin mRNA was translated in a rabbit reticulocyte cell-free system. Addition of tRNA from silk glands was essential for complete translation of the fibroin polypeptide. (Mr approximately 400,000). Synthesis of full-sized product took at least 85 min. In addition to full-size product, a large number of smaller polypeptides were observed upon analysis by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Evidence is presented that these smaller polypeptides are growing fibroin chains that transiently accumulate as discrete size classes due to discontinuities in the translation process. These discontinuities, or pauses, occur at specific sites in the fibroin mRNA template. The relative duration of the pauses can be experimentally modulated by changing the source of the supplementary tRNA added to the in vitro system. Silk glands were incubated in organ culture under conditions where essentially exclusive labeling of newly synthesized fibroins was attained. Analysis in sodium dodecyl sulfate gels showed that the labeling pattern of nascent silk fibroins is similar to the pattern observed in the reticulocyte cell-free system. This result suggests that discontinuities or pauses in polypeptide chain elongation also occur in vivo under conditions of organ culture.

Animals↗
PubMed1977

Delayed hypotony, shallow anterior chamber, and choroidal detachment in the postoperative cataract eye. A comparative study of closure with 7-0 silk, 9-0 silk, and 9-0 nylon.

To determine the time relationships between hypotony, choroidal detachment, and shallowing of the anterior chamber, an initial 64 eyes closed with 7-0 black silk were studied with applanation tensions, indirect ophthalmoscopy, and slit lamp examinations before surgery and for six weeks after cataract extraction. Applanation tension less than 6 mm Hg was detected in 72% of eyes, choroidal detachment in 44%, and shallowing of the anterior chamber in 28%. Low intraocular pressure was always detected at the same time or before either choroidal detachment or shallow anterior chamber. The peak period when pressure dropped to less than 6 mm Hg was shortly before 12 to 14 day suture removal or the day after. Suture tract leakage appears to be the predominant mechanism triggering this hypotony. Hypotony is prolonged past the leakage period, probably by ciliary body detachment. This 7-0 silk closure group is compared with 53 eyes closed with 9-0 virgin silk and 45 eyes closed with 9-0 nylon. Both of these latter groups showed substantially lower incidences of hypotony, choroidal detachment, and shallowing of the anterior chamber.

Anterior Chamber↗
PubMed1976

Studies on silk fibroin of Bombyx mori. I. Fractionation of fibroin prepared from the posterior silk gland.

1. Fractionation of fibroin prepared from the posterior silk glands of Bombyx mori was carried out. After carboxymethylation of the fibroin, it was fractionated by ammonium sulfate precipitation, Sephadex G-200 gel filtration and DEAE-cellulose column chromatography. 2. The fibroin was composed of at least two protein groups of large molecular size and three or four components of small molecular size, and, in addition, a mixture of proteins ranging in size from about 25,000 to more than 100,000 daltons with almost the same amino acid compositions. 3. The latter proteins contained about 48% glycine, 32% alanine, 11% serine, 4.5% tyrosine, 2% valine, and other minor amino acids. The sum of these main five amino acids accounts for more than 97% of the total amino acid residues of the proteins. 4. The present results indicate major heterogeneity in the molecular size of posterior silk gland fibroin, and, in addition, suggest the possibility of repeating sequences with relatively simple amino acid compositions in major peptide chains of fibroin.

Amino Acids↗
PubMed1976

Studies on the posterior silk gland of the silkworm Bombyx mori. V. Electron microscope localization of fibroin in the posterior silk gland at the later stage of the fifth instar.

Electron microscope observations of thin sections of epoxy resin-embeded posterior silk gland cells at the later stage of the fifth instar revealed that the Golgi vacuoles and the secretory granules (fibroin globules) in the cytoplasm and the glandular lumen contain fine fibrous materials. In frozen thin sections these structures appear as electron-dense granules and electron-dense blocks, or a column, respectively. Immunoelectron microscopy has shown that ferritin particles or products of the peroxidase reaction are localized on these structures. It was concluded that the fine fibrous materials most probably represent native fibroin molecules or their aggregates.

Animals↗
PubMed1976

Studies on the posterior silk gland of the silkworm Bombyx mori. VI. Distribution of microtubules in the posterior silk gland cells.

There are two microtubule systems in the posterior silk gland cells. One is a radial microtubule system in which the microtubules run radially from the basal to the apical cytoplasm and in which fibroin globules (secretory granules of fibroin) and mitochondria are arranged along these microtubules, thus composing a "canal system" which is assumed to be responsible for the intracellular transport of fibroin globules. The other is a circular microtubule system in the apical cytoplasm which is composed of bundles of microtubules and microfilaments running in a circular arrangement around the glandular lumen at an interval of approximately 4 mum at the end of the fifth instar. This system is presumably concerned with secretion and/or intraluminal transport of fibroin.

Animals↗
PubMed1991

Conformational energy studies of beta-sheets of model silk fibroin peptides. I. Sheets of poly(Ala-Gly) chains.

A new model structure is proposed for the silk I form of the crystalline domains of Bombyx mori silk fibroin and the corresponding crystal form of poly(L-Ala-Gly). It was deduced from conformational energy computations on stacked sheet structures of poly(L-Ala-Gly). The novel sheet structure contains interstrand hydrogen bonds but is composed of anti-parallel polypeptide chains whose conformation differs from that of the antiparallel beta-sheets that constitute the silk II structure. The strands of the new sheet have a two-residue repeat, in which the Ala residues adopt a right-handed and the Gly residues a left-handed sheet-like conformation. The computed unit cell is orthorhombic, with cell dimensions a = 8.94 A, b = 6.46 A, and c = 11.26 A. The model accounts for most spacings in the observed fiber x-ray diffraction patterns of silk I and of the silk-I-like form of poly(L-Ala-Gly), and it is consistent with nmr and ir spectroscopic data. As a test of the computations, the well-established beta-sheet structure of silk II and the corresponding form of poly(L-Ala-Gly) have been reproduced. The computed energies for the two forms of poly(L-Ala-Gly) indicate that the silk-II-like form is more stable, by about 1.0 kcal/mol per residue. The main difference between the two structures is the orientation of the Ala side chains of neighboring strands in each sheet. In the Pauling-Corey beta-sheet and in the silk II form, referred to as an "in-register" structure, the Ala side chains of every strand point to the same side of a sheet. In the silk I structure, referred to as "out-of-register," the side chains of Ala residues in adjacent strands point to opposite sides of the sheet.

Amino Acid Sequence↗
PubMed2025

De Novo Whole Genome Assemblies of Unusual Case-Making Caddisflies (Trichoptera) Highlight Genomic Convergence in the Composition of the Major Silk Gene (h-fibroin).

Trichoptera (caddisflies) is one of the most species-rich orders of aquatic insects. Species of caddisflies cover a broad ecological diversity as exemplified by various uses of underwater silk secretions. Diversity of silk use generally aligns with the evolution of major caddisfly lineages, specifically at the subordinal level: Annulipalpia (retreat makers) and Integripalpia (cocoon and tube-case makers). However, silk use within suborders differs for a few exceptional species in these clades. In this study, we provide the first whole genome assemblies and annotations for two unusual Integripalpia species: Limnocentropus insolitus, whose hard tube-case is anchored to boulders by a rigid, elongated silken stalk, and Phryganopsyche brunnea which builds a "floppy" cylindrical case that lacks the typical robustness of tube-cases. Its texture rather resembles that of the flexible retreats built by Annulipalpia. Using the two high-quality genome assemblies, we identified and annotated the major silk gene, h-fibroin, and compared its amino acid composition across various groups, including retreat, cocoon, and tube-case makers. Our phylogenetic analysis confirmed the phylogenetic position of the two species in the tube-case-making clade. The major silk gene of L. insolitus shows a similar amino acid composition to other tube-case-making species. In contrast, the amino acid composition of P. brunnea resembles that of retreat-making species, in particular with regard to the high content of proline. This is consistent with the hypothesis that proline could be linked to enhanced extensibility of silk fibers. Taken together, our results underscore the role of silk genes in shaping the evolutionary ecology of retreat- and tube-case-making in caddisflies.

Animals↗
PubMedDate not supplied

Bacterial adherence to cotton and silk sutures.

BACKGROUND: Silk and cotton sutures are the most commonly used materials for skin closure, the choice being largely based on tradition. We undertook this study to compare the bacterial adherence in vitro to these two materials because it is well known that the physicochemical characteristics of a suture material influence its ability to attract bacteria and consequently promote wound infection. METHODS: We determined the bacterial adherence in vitro to cotton and silk for Staphylococcus aureus and Escherichia coli, common organisms found in postoperative infection at our institute, using three inoculum strengths. The sutures were incubated with the organisms and bacterial counts per suture material calculated after 20, 60, 120 and 180 hours of incubation. The bacterial counts for the sutures were then compared at these intervals. RESULTS: The bacterial adherence for both organisms at all time intervals was significantly greater to silk than to cotton, except at 60 hours for Staphylococcus aureus. The bacterial count for each suture material appeared to be an intrinsic property of the suture and did not vary with the concentration of the bacteria in the initial inoculum. The cost of an equivalent thickness of silk is 50 times that of cotton. CONCLUSION: We suggest that cotton should be the preferred suture for skin closure because bacterial adherence to it is lower and it is much cheaper than silk.

Bacterial Adhesion↗
PubMed1992

Chemical modification of arginyl residues in silk fibroin: 1. Reaction of 1,2-cyclohexanedione in borate buffer.

Chemical modifications of silk fibroin were attempted in order to add new properties and functions to silk fibroin. The arginyl residue in solubilized silk fibroin was chemically modified with the reaction of 1,2-cyclohexanedione in borate buffer. FT-i.r. and c.d. spectra of the silk fibroin before and after the modification indicated that the fraction of random coil conformation increased with the modification. The chemical stability of the modified silk fibroin membrane was investigated in vitro with phosphate buffer. The modified arginyl residue in the membrane was considerably regenerated with the treatment in phosphate buffer.

Animals↗
PubMed1977

[Studies on protein biosynthesis in the silk gland of Bombyx mori L. silkworm].

The incorporation of (14C) lysine (to characterize the biosynthesis of cellular proteins) and (14C) glycine (for silk fibroin) in free and membrane-bound polyribosomes was studied in fibroin portion of the silk gland of Bombyx mori silkworm in the V instar. It was shown that although the membrane-bound polyribosomes are found in posterior silk gland from the beginning of the V instar, the fibroin biosynthesis in the membranebound polyribosomes takes place predominantly in the second part of the V instar. On the other hand the cellular proteins are synthesized mostly in the free polyribosomes in the first half of the V instar. In the second half of the V instar in the sucrose gradient zone corresponding to free polyribosomes, monoribosomes unable to synthesize protein for the absence of mRNA are present. Nevertheless, these ribosomes isolated from the fibroin part of the silk gland in the end of the V instar do synthesize polyphenylalanine in the presence of poly (U), and aminoacyl-t-RNA-synthetases and tRNA's obtained from the posterior silk gland.

Amino Acyl-tRNA Synthetases↗
PubMed1992

P25 gene regulation in Bombyx mori silk gland: two promoter-binding factors have distinct tissue and developmental specificities.

The gene encoding the silk protein P25 is expressed in the posterior silk gland of Bombyx mori with strict territorial and developmental specificities. The cis-acting regulatory elements previously located within the 441-bp 5' proximal sequence of the gene were examined for protein-binding capacities. We identified two factors, BMFA and SGFB, that lead to prominent band shifts and the target sites for which are included in a region homologous to the fibroin gene enhancer sequence. Analysis of the tissue-specific incidence of both factors showed that BMFA is ubiquitous, whereas SGFB is restricted to the silk gland cells. However, SGFB was found in both posterior and middle silk gland cells and therefore likely directs organ-specific, but not territory-specific, expression. Developmental studies throughout the fourth larval molt, at which the P25 gene status changes from derepressed to repressed, revealed that BMFA is reversibly modified at the transition from intermolt to molt. Indeed, the preexisting BMFA is replaced by a structurally related factor, BMFA', during the 2 h following head capsule apolysis. The exact temporal coincidence of this conversion with the onset of gene repression suggests that BMFA' is involved in transcription inactivation and likely results from a transduction process initiated by the hormonal change at molting.

Animals↗
PubMed1979

The chemical structure and the crystalline structures of Bombyx mori silk fibroin.

Some recent data (i.e. published in the last ten years) on the chemical and crystalline structures of B. mori silk are reviewed. The main emphasis is put on the crystallizable portion of silk fibroin, including its chemical constitution and its molecular conformation (at the crystallographic unit-cell level) in the two crystalline modifications : the beta pleated sheet and the silk I structures. The structural aspects are based on a discussion of X-ray and electron diffraction data, and on conformational energy analyses of a model (Ala-Gly)n polypeptide of silk fibroin.

Amino Acid Sequence↗
PubMed1979

Juvenile hormone modifies larvae and silk gland development in Bombyx mori.

Topical application of a Juvenile Hormone Analogue (ZR 515) during the first half of the first half of the last (fifth) larval instar of Bombyx mori induces a prolongation of this instar and increases larvae weight and silk secretion. Later treatment can lead to an extra larval molt. Moreover, the hormone analogue stops either the development or the secretory activity of the silk gland, depending on the period of treatments. When Juvenile Hormone is administered at the beginning of the fifth instar, silk gland growth as well as RNA and protein syntheses are first inhibited and later resumed and amplified. Finaly silk production increases up to 150 per cent of controls. One of the primarly effects of treatments seems to be RNA synthesis. Thus Juvenile Hormone analogue application could be a new tool for studying RNA transcription and/or processing.

Animals↗