Evidence of Decoupling Protein Structure from Spidroin Expression in Spider Dragline Silks

Abstract

The exceptional strength and extensibility of spider dragline silk have been thought to be facilitated by two spidroins, major ampullate spidroin 1 (MaSp1) and major ampullate spidroin 2 (MaSp2), under the assumption that protein secondary structures are coupled with the expressed spidroins. We tested this assumption for the dragline silk of three co-existing Australian spiders, Argiope keyserlingi, Latrodectus hasselti and Nephila plumipes. We found that silk amino acid compositions did not differ among spiders collected in May. We extended these analyses temporally and found the amino acid compositions of A. keyserlingi silks to differ when collected in May compared to November, while those of L. hasselti did not. To ascertain whether their secondary structures were decoupled from spidroin expression, we performed solid-state nuclear magnetic resonance spectroscopy (NMR) analysis on the silks of all spiders collected in May. We found the distribution of alanine toward β-sheet and 3,10helix/random coil conformations differed between species, as did their relative crystallinities, with A. keyserlingi having the greatest 3,10helix/random coil composition and N. plumipes the greatest crystallinity. The protein secondary structures correlated with the mechanical properties for each of the silks better than the amino acid compositions. Our findings suggested that a differential distribution of alanine during spinning could decouple secondary structures from spidroin expression ensuring that silks of desirable mechanical properties are consistently produced. Alternative explanations include the possibility that other spidroins were incorporated into some silks.

Multiscale mechanisms of nutritionally induced property variation in spider silks

“…Accordingly, 48 frames were collected per treatment per species, i.e. 6 frames x 8 individual threads (see [ 26 , 52 ] for details).…”

“…One randomly selected frame of silk from each thread (i.e. one of the six frames of silk collected per spider) was used to ascertain the width of the thread [ 26 , 52 ] so we could calculate the cross-sectional area of the individual threads used in the ensuing tensile tests. We taped the frames to a microscope slide and examined and photographed them under air immersion at 1000x magnification using a polarized light microscope (CKX41, Olympus, Tokyo, Japan) connected to a SPOT Idea 5 Mp digital camera (Spot Imaging Solutions, Sterling Heights, MI, USA).…”

“…We performed the following tensile tests under controlled temperature (~25°C) and humidity (~50% R.H.) in still air within 10 days of silk collection. We placed each of the cardboard frame-mounted silks for each species within the grips of an Instron 5543 tensile testing machine (Instron Machines, Melbourne, Australia) with a ~2μN resolution [ 26 ]. We ensured that the grips held the silks firmly at the upper and lower frame edges.…”

Major ampullate silk gland transcriptomes and fibre proteomes of the golden orb-weavers, Nephila plumipes and Nephila pilipes (Araneae: Nephilidae)

“…plumipes have reported on the mechanical properties of their silk, the relationship between protein secondary structure and primary amino acid sequence, populations in the urban environment, and copulation behaviour, however, no transcriptome data is available on the MA gland of this species, and only a handful of silk sequences are available for N . pilipes in online databases [ 36 – 42 ]. In this study, we report on a silk-gland specific transcriptome analysis for these golden orb-weaving species, N .…”

Clarity of objectives and working principles enhances the success of biomimetic programs

“…Detailed studies have established the links between the expression of certain spider silk genes and the proteins (spidroins) produced [54][55][56][57][58][59][60]. The properties of the silks are described across species, so we know that: (i) the spidroins form crystalline and non-crystalline nanostructures that respectively contribute to the silk's strength and extensibility [54][55][56][57], and; (ii) the amino acid composition of the spidroins correlates well with certain nanostructures [54,[59][60][61][62]. Dragline silk is manufactured in the major ampullate gland, which consists of three subsections that serve spidroin production, storage of the liquid precursor (dope) and fibre formation respectively (figure 2(a)).…”