title: Convergently-evolved structural anomalies in the coiled coil domains of insect silk proteins.
abstract: The use of coiled coil proteins as the basis of silk materials is an engineering solution that has evolved convergently in at least five insect lineages-the stinging hymenopterans (ants, bees, hornets), argid sawflies, fleas, lacewings, and praying mantises-and persisted throughout large radiations of these insect families. These coiled coil silk proteins share a characteristic distinct from other coiled coil proteins, in that they are fabricated into solid materials after accumulating as highly concentrated solutions within dedicated glands. Here, we relate the amino acid sequences of these proteins to the secondary and tertiary structural information available from biophysical methods such as X-ray scattering, nuclear magnetic resonance and Raman spectroscopy. We investigate conserved and convergently evolved features within these proteins and compare these to the features of classic coiled coil proteins including tropomyosin and leucine zippers. Our analysis finds that the coiled coil domains of insect silk proteins have several common structural anomalies including a high prevalence of alanine residues in core positions. These atypical features of the coiled coil fibrous proteins - which likely produce deviations from canonical coiled-coil structure - likely exist due to selection pressures related to the process of silk fabrication and the final function of the proteins.
authors.affiliation: Ecosystem Sciences, CSIRO, Australia. Electronic address: Tara.Sutherland@csiro.au.
authors.forename: Tara D
authors.initials: TD
authors.lastname: Sutherland
authors.affiliation: Ecosystem Sciences, CSIRO, Australia.
authors.forename: Holly E
authors.initials: HE
authors.lastname: Trueman
authors.affiliation: Ecosystem Sciences, CSIRO, Australia; Research School of Biology, Australian National University, Australia.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Walker
authors.affiliation: Ecosystem Sciences, CSIRO, Australia.
authors.forename: Sarah
authors.initials: S
authors.lastname: Weisman
authors.affiliation: Ecosystem Sciences, CSIRO, Australia.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Campbell
authors.affiliation: Ecosystem Sciences, CSIRO, Australia; State Key Laboratory of Silkworm Genome Biology, Southwest University, China.
authors.forename: Zhaoming
authors.initials: Z
authors.lastname: Dong
authors.affiliation: Materials Science and Engineering, CSIRO, Australia.
authors.forename: Mickey G
authors.initials: MG
authors.lastname: Huson
authors.affiliation: Materials Science and Engineering, CSIRO, Australia.
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Woodhead
authors.affiliation: Materials Science and Engineering, CSIRO, Australia.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Church
mesh_terms: D000409:Alanine / Q000737:chemistry; D019143:Evolution, Molecular; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D047011:Silk / Q000737:chemistry*
chemical_list: D047011:Silk; D000409:Alanine
keywords: Cocoons; Coiled coil; Helices; Insect; Protein; Silk