Abstract
Bombus terrestris, commonly known as the buff-tailed bumblebee, is native to Europe, parts of Africa and Asia. It is commercially bred for use as a pollinator of greenhouse crops. Larvae pupate within a silken cocoon that they construct from proteins produced in modified salivary glands. The amino acid composition and protein structure of hand drawn B. terrestris, silk fibres was investigated through the use of micro-Raman spectroscopy. Spectra were obtained from single fibres drawn from the larvae salivary gland at a rate of 0.14 cm/s. Raman spectroscopy enabled the identification of poly(alanine), poly(alanine-glycine), phenylalanine, tryptophan, and methionine, which is consistent with the results of amino acid analysis. The dominant protein conformation was found to be coiled coil (73%) while the β-sheet content of 10% is, as expected, lower than those reported for hornets and ants. Polarized Raman spectra revealed that the coiled coils were highly aligned along the fibre axis while the β-sheet and random coil components had their peptide carbonyl groups roughly perpendicular to the fibre axis. The protein orientation distribution is compared to those of other natural and recombinant silks. A structural model for the B. terrestris silk fibre is proposed based on these results.
Highlights
Over recent years, there has been a growing interest in natural and synthetic insect silks for their physical properties and biocompatibility
As expected from the analytical results obtained from bees and hornets [7,26], the 10% β-sheet content determined for the B. terrestris fibre is significantly less than the 24% content determined for hornet silk by infrared analysis [27]
The peptide carbonyl orientation distribution observed from hand drawn B. terrestris silk fibre has a similar shape but is at right angles to that observed for the N. edulis dragline silk
Summary
There has been a growing interest in natural and synthetic insect silks for their physical properties and biocompatibility. The aculeates (Hymenoptera, stinging insects) are an abundant group of insects that includes the social species of ants, hornets, and bees. While the proteins are largely coiled coil in conformation, significant level of β-sheet structure has been detected by X-ray diffraction, infrared, and/or solid state NMR analysis in the silks of native bees, ant and hornet silk, reconstituted hornet silk, and artificial honeybee silk. Since 1987 B. terrestris has been bred commercially for use as a pollinator for European greenhouse crops [8,9] It has been commercially reared in New Zealand since the early 1990s [10,11] and is used in many countries and regions including North Africa, Japan, Korea, and Russia [12]. A model for the protein structure of a typical B. terrestris silk fibre is proposed
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