The Transcriptome of Darwin's Bark Spider Silk Glands Predicts Proteins Contributing to Dragline Silk Toughness

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July 25, 2019

Jessica E. Garb, Robert A. Haney, Evelyn E. Schwager, Matjaž Gregorič, Matjaž Kuntner, Ingi Agnarsson & Todd A. Blackledge Communications Biology 2, Article number: 275 (2019)

The transcriptome of Darwin's bark spider silk glands predicts proteins contributing to dragline silk toughnessDarwin's bark spider (Caerostris darwini) spins largest orb webs using silk glands with unusually long spinning ducts.


Darwin's bark spider (Caerostris darwini) produces giant orb webs from dragline silk that can be twice as tough as other silks, making it the toughest biological material. This extreme toughness comes from increased extensibility relative to other draglines. We show C. darwinidragline-producing major ampullate (MA) glands highly express a novel silk gene transcript (MaSp4) encoding a protein that diverges markedly from closely related proteins and contains abundant proline, known to confer silk extensibility, in a unique GPGPQ amino acid motif. This suggests C. darwini evolved distinct proteins that may have increased its dragline's toughness, enabling giant webs. Caerostris darwini's MA spinning ducts also appear unusually long, potentially facilitating alignment of silk proteins into extremely tough fibers. Thus, a suite of novel traits from the level of genes to spinning physiology to silk biomechanics are associated with the unique ecology of Darwin’s bark spider, presenting innovative designs for engineering biomaterials.

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