The Silk Fibroins

Lucas, François; Shaw, J. T. B.; Smith, S. G.

doi:10.1016/s0065-3233(08)60599-9

Cited by 175 publications

(73 citation statements)

References 183 publications

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“…5). Side chain bulkiness, however, is not necessarily a problem in ␤-sheet formation since intersheet spacings as large as 10 Å occur in group IV and V silks (21). Another fibroin-like structure is the GAGA-rich sequence (residues 783 to 801) immediately preceding the C-terminal polyalanine runs in ␣-preCol-D (Fig.…”

Section: Resultsmentioning

confidence: 99%

Tough Tendons

Xx¹,

Coyne²,

Jh³

1997

Journal of Biological Chemistry

136

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The primary structure of the ␣-chain of preCol-D (molecular mass ‫؍‬ 80 kDa), a tanned collagenous protein predominating in the distal portion of the byssal threads of the mussel Mytilus edulis, was deduced from cDNA to encode an unprecedented natural block copolymer with three major domain types: a central collagen domain flanked by fibroin-like domains and followed by histidine-rich termini. The fibroin-like domains have sequence motifs that strongly resemble the crystalline polyalanine-rich and amorphous glycine-rich regions of spider dragline silk fibroins. The terminal regions resemble the histidine-rich domains of a variety of metalbinding proteins. The silk domains may toughen the collagen by increasing its strength and extensibility. PreCol-D expression is limited to the mussel foot, which contains a longitudinal gradient of preCol-D mRNA. This gradient increases linearly in the proximal to distal direction and reaches a maximum just before the distal depression of the foot.Marine mussels Mytilus edulis produce byssal threads to attach to solid surfaces in the turbulent intertidal zone. Each thread is stiff at one end and extensible at the other. Molecular gradients correlated with a stiff-to-extensible mechanical gradation exist along the length of each thread (1, 2). Byssal threads (Fig. 1A) are often compared with tendons on the basis of their construction from anisotropically oriented bundles of collagen fibrils (3). Indeed, the distal portion of byssus and tendon share a roughly similar tensile strength and initial stiffness (4), but the similarity ends there. Byssal threads are at least five times more extensible and five times tougher than Achilles tendon (5). Moreover, unlike tendon, byssal threads have a nonperiodic microstructure and shrinkage and melting temperatures in excess of 90°C (6). Understanding how byssal collagen differs from other collagens is a critical first step to appreciating its role in the material performance of byssus.The characterization of byssal collagens has long been thwarted by the intractable cross-linked nature of byssus. Two independent lines of evidence, however, have hinted at an unusual possibility: that byssal collagen may be endowed with some qualities of a silk fibroin-like structure. The first evidence is based on wide-angle fiber x-ray diffraction of byssal threads of Mytilus edulis. The distal part consistently exhibits a typical collagen diffraction pattern with the notable addition of strong equatorial reflections at 4.5-4.6 Å and nonaxial arcs at 3.7-3.8 Å (2, 7). These prompted Rudall (7) to suggest the presence of a ␤-phase in the byssal collagen or an additional ␤-protein in the distal portion of byssus.In the second line of evidence, byssal threads of M. edulis were subjected to acid extraction coupled with extensive pepsinization. This approach solubilized two collagenous fragments, Col-P 1 and Col-D (both apparently homotrimers), predominating at the proximal and distal end of each thread, respectively (1). Precursors of these fragments, preCol-P ...

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Section: Resultsmentioning

confidence: 99%

Tough Tendons

Xx¹,

Coyne²,

Jh³

1997

Journal of Biological Chemistry

136

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“…11,17 Silk from the silkworm Bombyx mori has been extensively studied and is a fibrous protein consisting of a repeating sequence of (GAGAGS) somewhat similar in composition to spider silk and contains Gly (43.7%), Ala (28.8%), and Ser (11.9%). 18 NMR and other biophysical studies of B. mori and other silkworm silks have provided secondary structure information. In particular, solid-state NMR has been applied to silkworm silk to investigate molecular orientation using isotopically labeled amino acids: 13 C, 11,19-23 15 N, 20,23 and 2 H to study the hydrogen bonding structure.…”

Section: Introductionmentioning

confidence: 99%

Orientational order of Australian spider silks as determined by solid‐state NMR

et al. 2006

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A simple solid-state NMR method was used to study the structure of 13 C-and 15 Nenriched silk from two Australian orb-web spider species, Nephila edulis and Argiope keyserlingi. Carbon-13 and 15 N spectra from alanine-or glycine-labeled oriented dragline silks were acquired with the fiber axis aligned parallel or perpendicular to the magnetic field. The fraction of oriented component was determined from each amino acid, alanine and glycine, using each nucleus independently, and attributed to the ordered crystalline domains in the silk. The relative fraction of ordered alanine was found to be higher than the fraction of ordered glycine, akin to the observation of alanine-rich domains in silk-worm (Bombyx mori) silk. A higher degree of crystallinity was observed in the dragline silk of N. edulis compared with A. keyserlingi, which correlates with the superior mechanical properties of the former #

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“…The demand for fibroin, the principal protein of silk, requires highly efficient transcription and translation of the fibroin gene in cells of the silk gland. Translational efficiency in these cells is maximized by the quantitative adaptation of the tRNA population to the composition of fibroin: 44% glycine, 29% alanine, and 12% serine (5,29,30,42). In the case of tRNA Ala , enrichment is achieved both by increasing the level of the constitutive type of tRNA Ala (tRNA C Ala ) and by synthesizing an additional, silk gland-specific, type (tRNA SG Ala ) (31,44).…”

mentioning

confidence: 99%

TATA-Binding Protein–TATA Interaction Is a Key Determinant of Differential Transcription of Silkworm Constitutive and Silk Gland-Specific tRNA^Ala Genes

Ouyang

Martinez

Young

et al. 2000

Molecular and Cellular Biology

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We have investigated the contribution of specific TATA-binding protein (TBP)-TATA interactions to the promoter activity of a constitutively expressed silkworm tRNA C Ala gene and have also asked whether the lack of similar interactions accounts for the low promoter activity of a silk gland-specific tRNA SG Ala gene. We compared TBP binding, TFIIIB-promoter complex stability (measured by heparin resistance), and in vitro transcriptional activity in a series of mutant tRNA C Ala promoters and found that specific TBP-TATA contacts are important for TFIIIB-promoter interaction and for transcriptional activity. Although the wild-type tRNA C Ala promoter contains two functional TBP binding sequences that overlap, the tRNA SG Ala promoter lacks any TBP binding site in the corresponding region. This feature appears to account for the inefficiency of the tRNA SG Ala promoter since provision of either of the wild-type TATA sequences derived from the tRNA C Ala promoter confers robust transcriptional activity. Transcriptional impairment of the wild-type tRNA SG Ala gene is not due to reduced incorporation of TBP into transcription complexes since both the tRNA C Ala and tRNA SG Ala promoters form transcription complexes that contain the same amount of TBP. Thus, the deleterious consequences of the lack of appropriate TBP-TATA contacts in the tRNA SG Ala promoter must come from failure to incorporate some other essential transcription factor(s) or to stabilize the complete complex in an active conformation.The silkworm Bombyx mori provides a clear example of regulated tRNA gene expression. The demand for fibroin, the principal protein of silk, requires highly efficient transcription and translation of the fibroin gene in cells of the silk gland. Translational efficiency in these cells is maximized by the quantitative adaptation of the tRNA population to the composition of fibroin: 44% glycine, 29% alanine, and 12% serine (5,29,30,42). In the case of tRNA Ala , enrichment is achieved both by increasing the level of the constitutive type of tRNA Ala (tRNA C Ala ) and by synthesizing an additional, silk gland-specific, type (tRNA SG Ala ) (31,44). In vitro studies of representative tRNA C Ala and tRNA SG Ala genes have revealed transcription properties consistent with the patterns of tRNA C Ala and tRNA SG Ala accumulation in vivo. That is, in a variety of extracts from non-silk gland cells, the tRNA C Ala gene directs transcription much more efficiently than does the tRNA SG Ala gene, but in concentrated extracts from silk gland, the two genes are equally efficient (60). To understand how these two genes are differentially regulated, we have investigated the basis of the transcriptional impairment of the tRNA SG Ala gene that is observed under typical in vitro conditions. Transcription of silkworm tRNA Ala genes is driven by both internal and external promoter elements (26,36,56). The critical difference between the tRNA C Ala and tRNA SG Ala genes is in the interaction of their 5Ј flanking promoter elements with the transcri...

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The Silk Fibroins

Cited by 175 publications

References 183 publications

Tough Tendons

Tough Tendons

Orientational order of Australian spider silks as determined by solid‐state NMR

TATA-Binding Protein–TATA Interaction Is a Key Determinant of Differential Transcription of Silkworm Constitutive and Silk Gland-Specific tRNA^Ala Genes

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The Silk Fibroins

Cited by 175 publications

References 183 publications

Tough Tendons

Tough Tendons

Orientational order of Australian spider silks as determined by solid‐state NMR

TATA-Binding Protein–TATA Interaction Is a Key Determinant of Differential Transcription of Silkworm Constitutive and Silk Gland-Specific tRNAAla Genes

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TATA-Binding Protein–TATA Interaction Is a Key Determinant of Differential Transcription of Silkworm Constitutive and Silk Gland-Specific tRNA^Ala Genes