title: 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.
authors: Evolution & Ecology Research Centre, School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney 2052, Australia. s.blamires@unsw.edu.au.
authors: Sean J
authors: SJ
authors: Blamires
authors: Evolution & Ecology Research Centre, School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney 2052, Australia. m.kasumovic@unsw.edu.au.
authors: Michael M
authors: MM
authors: Kasumovic
authors: Department of Life Science, Tunghai University, Taichung 40704, Taiwan. spider@thu.edu.tw.
authors: I-Min
authors: IM
authors: Tso
authors: Graduate School of Biomedical Engineering, University of New South Wales, Sydney 2052, Australia. p.martens@unsw.edu.au.
authors: Penny J
authors: PJ
authors: Martens
authors: NMR Facility, Mark Wainwright Analytical Centre, University of New South Wales, Sydney 2052, Australia. j.hook@unsw.edu.au.
authors: James M
authors: JM
authors: Hook
authors: NMR Facility, Mark Wainwright Analytical Centre, University of New South Wales, Sydney 2052, Australia. a.rawal@unsw.edu.au.
authors: Aditya
authors: A
authors: Rawal
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005349:Fibroins / Q000737:chemistry*; D019476:Insect Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D047011:Silk / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D019476:Insect Proteins; D047011:Silk; C086087:spidroin 1; D005349:Fibroins
keywords: amino acids; high performance liquid chromatography; mechanical properties; orb weaving spiders; protein secondary structures; silk spinning; solid-state nuclear magnetic resonance spectroscopy