Extreme Diversity, Conservation, and Convergence of Spider Silk Fibroin Sequences

Abstract

Spiders (Araneae) spin high-performance silks from liquid fibroin proteins. Fibroin sequences from basal spider lineages reveal mosaics of amino acid motifs that differ radically from previously described spider silk sequences. The silk fibers of Araneae are constructed from many protein designs. Yet, the repetitive sequences of fibroins from orb-weaving spiders have been maintained, presumably by stabilizing selection, over 125 million years of evolutionary history. The retention of these conserved motifs since the Mesozoic and their convergent evolution in other structural superproteins imply that these sequences are central to understanding the exceptional mechanical properties of orb weaver silks.

The Nephila clavipes genome highlights the diversity of spider silk genes and their complex expression

“…2b). The overall diversity and complexity of these repetitive structures were greater than expected, considering previous reports 29 .…”

“…One motif group consisted of GXGGX-containing motif variants, including the well-known motif variant GPGGY 18,29 (Fig. 2a).…”

“…Many spider species produce just a subset of these silk classes, and some produce yet other silk types, including cribellate silk 25 . Each species possesses an assortment of specialized gland types that are thought to produce distinct classes of silks to fit specific needs 9,26,27 .Spider silks are composed primarily of spidroin proteins (where a 'spidroin' is a spider fibroin [28][29][30][31] ) that, by convention, have been named and classified according to the specific silk gland in which they were first discovered. Spidroin proteins have conserved N-and C-terminal domains that flank long runs of repeated motifs 32-34 , the composition and number of which confer specific physical properties to silks 27 .…”

“…Spider silks are composed primarily of spidroin proteins (where a 'spidroin' is a spider fibroin [28][29][30][31] ) that, by convention, have been named and classified according to the specific silk gland in which they were first discovered. Spidroin proteins have conserved N-and C-terminal domains that flank long runs of repeated motifs [32][33][34] , the composition and number of which confer specific physical properties to silks 27 .…”

“…1a-c). The first spidroins were characterized from N. clavipes [28][29][30][31] , and this species has continued to be useful for investigating silk genes, their diversity and structure, and their evolutionary history as a gene family 29 . Surprisingly, the full genome of this extensively studied species, the "ubiquitous workhorse of spider research" (ref.…”