Spiders use aciniform silk to wrap and immobilize their prey and also in the construction of egg cases. It is the finest of the spider silks having a fiber diameter approximately an order of magnitude smaller compared to spider dragline silk. For the spider species Argiope aurantia, we find aciniform silk fiber diameters are 500 ± 100 nm compared to 3.5 ± 0.5 µm for dragline spider silk (see Figure 1). Aciniform spider silk has been scarcely studied compared to other spider and silkworm silks. Yet, it has been shown that the mechanical properties are superior compared to the highly touted dragline silk with regards to toughness because of a unique combination of high modulus and extensibility.1,2 There is some primary amino acid sequence information available on the protein that comprises aciniform spider silk, aciniform spidroin 1 (AcSp1), that illustrates it is a highly repetitive protein similar to other spider silk proteins, but lacks the common repeat units found in other spider silks. For example, the poly(Ala) and Gly-Ala couplets that form the nanocrystalline β-sheet structures that impart dragline spider silk its high modulus are poorly represented in the primary amino acid sequence of AcSp1.1 By feeding the spiders 13C/15N-labeled amino acids we can label the prey wrap silk enabling advanced mulidimesional magic angle spinning (MAS) solid-state NMR techniques to characterize the silk protein structure. We find that this silk, unlike other spider and silkworms silks, has a predominat α-helical structure compared to the β-sheet hallmark structure of other spider and silkworm silks. This structural information helps to explain the greater extensibility and toughness observed for prey wrap spider silk compared to the dragline silk. (1) Hayashi et al. Molecular Biology and Evolution 2004, 21, 1950-1959. (2) Blackledge et al. J. Exp. Biol. 2006, 209, 2452-2461.

Investigating the unique structure and physical properties of spider prey wrap silk with electron microscopy and solid-state NMR

251st National Meeting (2016)

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