Spiders possess a singular ability to strike irrational fear; perhaps none so much as the much-maligned black widow. However, these misunderstood creatures may be key to the development of high-performance, environmentally-friendly synthetic fibers. Scientists are especially interested in how these spiders spin their webs, pursuing this knowledge by profiling amino acid sequencing, screening cDNA libraries, and employing proteomic analyses to both silk fibers and silk-producing glands of some spider species (orbweaver Nephila clavipes and cobweaver Latrodectus hesperus, commonly referred to as the black widow).
Two recent mass spectrometric studies called into question the established belief that spider-sourced dragline silk comprises a two-protein fiber (major ampullate spidroins, MaSp 1 and 2). These studies identified two other components of dragline silk- low molecular weight cysteine-rich protein 1 (CRP1)1 and aciniform spidroin 1 (AcSp1).2 Perhaps even more compelling, the findings suggested that spiders actually modify their fibers by altering silk gene expression and protein composition.
To enhance the overall understanding of the protein components of dragline silk, Larracas et al. (2016)3 fed black widows for two to three weeks before collecting their silk and subjecting them to dissection under anesthesia. After peeling back the exoskeleton, the scientists harvested pairs of silk glands (major ampullate, MA glands). They reserved one of these for proteomic analysis and skinned the second to collect pure spinning dope. The research team dissolved the harvested components (silk, spinning dope, and glands) in solvent before tryptic digestion and analysis by liquid chromatography mass spectrometry (LC-MS) combining a Dionex Ultimate 3000 autosampler, Orbitrap Fusion Tribrid mass spectrometer, and Xcalibur 4.0 software (all Thermo Scientific).
The researchers first investigated the performance of different solvents, employing three MS/MS dissociation modes (collision-induced dissociation- CID, electron transfer dissociation- ETD, and high energy collision dissociation- HCD) to maximize protein identifications. Looking at each treatment separately, the team combined the three sets of spectral data and searched the annotated UniProt Latrodectus database and, when necessary, the unannotated Latrodectus transcriptome database via Proteome Discoverer 2.1 (Thermo Scientific). They produced a composite list of 28 unique proteins in dragline silk, including 20 annotated proteins and eight unannotated proteins. They reported on solvent efficiency as follows: HFIP (hexafluoroisopropanol) treatment produced the greatest number of peptides with coverage for MaSps, AcSp1, CRPs, and CRISP3. Other efficient solvents were GITC (guanidium thiocyanate) and LiBr (lithium bromide). Urea was the least efficient solvent despite its common usage for this purpose.
Larracas et al. reported identification of 66 distinct proteins in the MA gland (56 unique to the MA gland), 14 distinct proteins from the dragline fibers (five unique to the fibers), and 11 distinct proteins from the spinning dope (three unique to the spinning dope). They highlighted identification of seven proteins common to all three: MaSp1, MaSp2, CRP1, CRP2, CRP4, CRISP3, and fasciclin.
The researchers offer these common proteins as targets ripe for further research, particularly in terms of their precise biological functions. Another area for further study is the possibility that black widows can alter silk gene expression in complex ways within the same gland, thereby producing composite fibers. Together, the data reported here and potential future investigations may enable the silk industry to produce synthetic fibers that more closely mimic natural spider silk. And there’s nothing creepy about that.
1 Pham, T. et al. (2014) ‘Dragline silk: A fiber assembled with low-molecular-weight cysteine-rich proteins.’ Biomacromolecules 15:4073–4081. doi: 10.1021/bm5011239.
2 Chaw, R.C. et al. (2015) ‘Proteomic evidence for components of spider silk synthesis from black widow silk glands and fibers.’ Journal of Proteome Research 14:4223–4231. doi: 10.1021/acs.jproteome.5b00353.
3 Larracas, C. et al. (2016) ‘Comprehensive Proteomic Analysis of Spider Dragline Silk from Black Widows: A Recipe to Build Synthetic Silk Fibers.’ International Journal of Molecular Sciences, 17(9): 1537, doi: 10.3390/ijms17091537
Post Author: Melissa J. Mayer. Melissa is a freelance writer who specializes in science journalism. She possesses passion for and experience in the fields of proteomics, cellular/molecular biology, microbiology, biochemistry, and immunology. Melissa is also bilingual (Spanish) and holds a teaching certificate with a biology endorsement.