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A: A worker hornet brood comb with pupal silk caps (1) and with larvae before pupation (2). B: Silk caps extracted from combs containing hornet pupae (seen by light microscopy). The large silk caps have been removed from queen pupae (Q), and the smaller ones from male pupae (M) (31). C: Silk fibers from a silk cap. At the center, one large silk fiber can be seen. It is composed of several silk fibers that have been attached together. The various silk fibers are deposited in all directions, but there are still gaps between them to allow gas exchange. D: A piece of the silk sleeve that envelops the pupa inside the comb cell. As can be seen the fibers are sparse and between
Source publication
In silk from the larval silk caps of the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae), temperature-dependent changes in the electric voltage have been recorded, with rise in the voltage occurring mainly upon rise in the temperature between 10-36 degrees C. The peak voltage was measured between 32-38 degrees C and attained 240-360 mV, bu...
Contexts in source publication
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... by IR photography that various silk caps in the same comb show different temperatures ((Litinetsky et al., 1998((Litinetsky et al., , 2001); Fig. 1)); and finally, whether the silk is sensitive to high temperatures. The present study attempts to provide some answers to the aforementioned points. The silk caps are made up mostly of fibers ( Fig. 2) and some plaques that connect some of them (see Fig. 2C) and the sleeve contains only a few fibers and many plaques (Fig. 2D). The fibers are about 10 lm in diameter and sometimes the coat peels off enabling (1) and with larvae before pupation (2). B: Silk caps extracted from combs containing hornet pupae (seen by light microscopy). ...
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... comb show different temperatures ((Litinetsky et al., 1998((Litinetsky et al., , 2001); Fig. 1)); and finally, whether the silk is sensitive to high temperatures. The present study attempts to provide some answers to the aforementioned points. The silk caps are made up mostly of fibers ( Fig. 2) and some plaques that connect some of them (see Fig. 2C) and the sleeve contains only a few fibers and many plaques (Fig. 2D). The fibers are about 10 lm in diameter and sometimes the coat peels off enabling (1) and with larvae before pupation (2). B: Silk caps extracted from combs containing hornet pupae (seen by light microscopy). The large silk caps have been removed from queen pupae ...
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... et al., , 2001); Fig. 1)); and finally, whether the silk is sensitive to high temperatures. The present study attempts to provide some answers to the aforementioned points. The silk caps are made up mostly of fibers ( Fig. 2) and some plaques that connect some of them (see Fig. 2C) and the sleeve contains only a few fibers and many plaques (Fig. 2D). The fibers are about 10 lm in diameter and sometimes the coat peels off enabling (1) and with larvae before pupation (2). B: Silk caps extracted from combs containing hornet pupae (seen by light microscopy). The large silk caps have been removed from queen pupae (Q), and the smaller ones from male pupae (M) (31). C: Silk fibers from a ...
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... so that the central fiber (i.e. the core) can be seen. F: An enlarged cross-section of one silk fiber. The envelope (sericin) has been reduced (by heat) to very small remnants (a). The main fiber is composed of two separate ones (arrow) that emerge from the labial (salivary) gland as one single fiber. the core to be seen under magnification (Fig. 2E). The core is made up of the unified fibers (Fig. ...
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... seen. F: An enlarged cross-section of one silk fiber. The envelope (sericin) has been reduced (by heat) to very small remnants (a). The main fiber is composed of two separate ones (arrow) that emerge from the labial (salivary) gland as one single fiber. the core to be seen under magnification (Fig. 2E). The core is made up of the unified fibers (Fig. ...
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... we deemed it worthwhile to ascertain whether and how the silk cap \maintains" its voltage over time in a fixed temperature. To this end, we examined the silk behavior voltage-wise at two fixed temperatures, namely 158C (Fig. 5A) and 208C (Fig. 5B). As can be seen from Figure 3A, in a cap held at a steady 158C, the voltage surged within 12 min to a peak of about 215 mV, then began to decline steeply at first (between the 15th and 45th min) down to about 150 mV and subsequently more gradually to below starting level (by the 90th min). At a steady 208C (Fig. 5B), peak voltage of ...
Citations
Organisms develop unique systems in a given environment. In the process of adaptation, they employ materials in a clever way, which has inspired mankind extensively. Understanding the behavior and material properties of living organisms provides a way to emulate these natural systems and engineer various materials. Silk is a material that has been with human for over 5000 years, and the success of mass production of silkworm silk has realized its applications to medical, pharmaceutical, optical, and even electronic fields. Spider silk, which was characterized later, has expanded the application sectors to textile and military materials based on its tough mechanical properties. Because silk proteins are main components of these materials and there are abundant creatures producing silks that have not been studied, the introduction of new silk proteins would be a breakthrough of engineering materials to open innovative industry fields. Therefore, in this review, we present diverse silk and silk-like proteins and how they are utilized with respect to organism's survival. Here, the range of organisms are not constrained to silkworms and spiders but expanded to other insects, and even marine creatures which produce silk-like proteins that are not observed in terrestrial silks. This viewpoint broadening of silk and silk-like proteins would suggest diverse targets of engineering to design promising silk-based materials.
Statement of significance
Silk has been developed as a biomedical material due to unique mechanical and chemical properties. For decades, silks from various silkworm and spider species have been intensively studied. More recently, other silk and silk-like proteins with different sequences and structures have been reported, not only limited to terrestrial organisms (honeybee, green lacewing, caddisfly, and ant), but also from marine creatures (mussel, squid, sea anemone, and pearl oyster). Nevertheless, there has hardly been well-organized literature on silks from such organisms. Regarding the relationship among sequence-structure-properties, this review addresses how silks have been utilized with respect to organism's survival. Finally, this information aims to improve the understanding of diverse silk and silk-like proteins which can offer a significant interest to engineering fields.
Hornet silks, fibrous proteins present in the cocoon produced by the larvae of vespa species, are composed of four major proteins. Complete amino acid sequences of the four major proteins (Vssilk 1-4) in the hornet silk produced by the yellow hornet ( Vespa simillima, Vespinae, Vespidae) have been determined. The amino acid sequences in Vssilk 1-4 are highly divergent, but the four proteins have some common properties. The most attractive feature of these proteins is that they have an alpha-helix region, which includes coiled-coil alpha-helices, and a beta-sheet region. The aforementioned coiled-coil and beta-sheet structures are responsible for the intermolecular binding between the Vssilk 1-4 proteins that make up the composite structure in hornet silk. This coiled-coil structure is restored when hornet silk gel films are formed by pressing and drying hornet silk hydrogel. Drawing-induced changes in the orientation and conformation of the coiled-coil structure are investigated in order to clarify the reason for the formation of this structure.
In this article, we review current knowledge about the silk produced by the larvae of bees, ants, and hornets [Apoidea and Vespoidea: Hymenoptera]. Different species use the silk either alone or in composites for a variety of purposes including mechanical reinforcement, thermal regulation, or humidification. The characteristic molecular structure of this silk is α-helical proteins assembled into tetrameric coiled coils. Gene sequences from seven species are available, and each species possesses a copy of each of four related silk genes that encode proteins predicted to form coiled coils. The proteins are ordered at multiple length scales within the labial gland of the final larval instar before spinning. The insects control the morphology of the silk during spinning to produce either fibers or sheets. The silk proteins are small and non repetitive and have been produced artificially at high levels by fermentation in E. coli. The artificial silk proteins can be fabricated into materials with structural and mechanical properties similar to those of native silks.
Wasps apparently develop normally even under extreme thermal conditions, including deserts. We deemed it worthwhile to set up an experiment wherein wasp brood combs containing a full gamut of brood ranging from eggs up to pupae and a few adults were kept in an incubator whose temperature was gradually raised to 45 degrees C, and the response of the disparate brood to such warming was photographed via Infra Red camera. The finding of this experiment showed that for open brood (i.e., eggs, larvae at various instars, and empty cells) the temperature was close to the ambient temperature, but in the silk coated pupae, the temperature was lower than the ambient by up to 4 degrees C. This lower temperature was retained for at least 90 min of incubation. For comparison we evaluated the relative contribution of the pupae to the phenomenon, by warming also a vacant, (i.e., a broodless and silkless comb) in parallel to a comb from which the pupae had been extricated but the silk weave retained and left behind. We found that the totally empty comb heated up under these conditions to nearly 110 degrees C, whereas the silk-containing vacant cells only heated up to about 40 degrees C. These finding are discussed from two aspects, namely the importance for wasps to maintain a constant temperature throughout the pupating process, and the manner in which the silk weave contributes to such a goal.
Hornet silk, a fibrous protein in the cocoon produced by the larva of the vespa, is composed of four major proteins. In this study, we constructed silk-gland cDNA libraries from larvae of the hornet Vespa simillima xanthoptera Cameron and deduced the full amino acid sequences of the four hornet silk proteins, which were named Vssilk 1-4 in increasing order of molecular size. Portions of the amino acid sequences of the four proteins were confirmed by Matrix-assisted laser desorption/ionization-time of flight/mass spectrometry (MALDI-TOF/MS) and N-terminal protein sequencing. The primary sequences of the four Vssilk proteins (1-4) were highly divergent, but the four proteins had some common properties: (i) the amino acid compositions of all four proteins were similar to each other in that the well-defined and characteristic repetitive patterns present in most of the known silk proteins were absent; and (ii) the characteristics of the amino acid sequences of the four proteins were also similar in that Ser-rich structures such as sericin were localized at both ends of the chains and Ala-rich structures such as fibroin were found in the center. These characteristic primary structures might be responsible for the coexisting alpha-helix and beta-sheet conformations that make up the unique secondary structure of hornet silk proteins in the native state. Because heptad repeat sequences of hydrophobic residue are present in the Ala-rich region, we believe that the Ala-rich region of hornet silk predominantly forms a coiled coil with an alpha-helix conformation.
