Evidence from Multiple Species that Spider Silk Glue Component ASG2 is a Spidroin

Abstract

Spiders in the superfamily Araneoidea produce viscous glue from aggregate silk glands. Aggregate glue coats prey-capture threads and hampers the escape of prey from webs, thereby increasing the foraging success of spiders. cDNAs for Aggregate Spider Glue 1 (ASG1) and 2 (ASG2) have been previously described from the golden orb-weaver, Nephila clavipes, and Western black widow, Latrodectus hesperus. To further investigate aggregate glues, we assembled ASG1 and ASG2 from genomic target capture libraries constructed from three species of cob-web weavers and three species of orb-web weavers, all araneoids. We show that ASG1 is unlikely to be a glue, but rather is part of a widespread arthropod gene family, the peritrophic matrix proteins. For ASG2, we demonstrate its remarkable architectural and sequence similarities to spider silk fibroins, indicating that ASG2 is a member of the spidroin gene family. Thus, spidroins have diversified into glues in addition to task-specific, high performance fibers.

Diet-induced covariation between architectural and physicochemical plasticity in an extended phenotype

“…It is the glycoprotein composition that primarily determines stickiness in orb web gluey silks (Sahni et al, 2014b). Henceforth the differential expression of aggregate glycoprotein (Choresh et al, 2009;Vasanthavada et al, 2012;Collin et al, 2016) remains a plausible alternative explanation for the differences in spiral stickiness between spiders in the cricket and cockroach feeding treatments. Spread and extension of the glycoproteins under load is, nevertheless, enhanced if the glycoproteins are sufficiently hydrated (Stellwagen et al 2014;Opell et al, 2015).…”

Towards Spider Glue: Long-read scaffolding for extreme length and repetitious silk family genes AgSp1 and AgSp2 with insights into functional adaptation

“…AgSp1 and AgSp2 are members of the spidroin protein family (Collin et al, 2016) and are encoded by the same general N-terminus/Repeat(n)/C-terminus pattern found in this family, however the size and internal organization are distinct. We have broken the predicted protein of each spidroin into several regions.…”

“…The C-terminal transition region is shorter than the N-terminal transition, and maintains the same organization as the internal repeats, with the majority of variation occurring towards the end of each repeat iteration. The C-terminus has been previously described (Choresh et al, 2009;Collin et al, 2016).…”

“…Initial evidence for aggregate glue gene sequences was derived from what were thought to be two full-length transcripts encoding the glue proteins of orb weaver Nephila clavipes (Linnaeus, 1767), and were named ASG1 (Aggregate Spider Glue; 1,221 bp) and ASG2 (2,145 bp) (Choresh et al, 2009). Several years later, it was determined that ASG1 expression is not unique to aggregate glands, and that the ASG2 sequence, while mostly correct, contained a short insertion (Collin et al, 2016). Collin et al (2016) also discovered that the predicted ASG2 C-terminus aligns with other spidroins, and it was suggested ASG2 be renamed to AgSp1 (Aggregate Spidroin 1) to follow gene family convention, which we have adopted here.…”

Molecular Structural Analysis of Spider’s Capture Thread and Viscid Droplets Studied by Microscopic FT-IR Spectroscopy

“…This result is consistent with recent reports. 20,21 Figure 4 compares the IR spectral changes of the capture thread with regard to water dissolving of viscid droplets. While the characteristic bands in the region of 1400 -1000 cm -1 arising from the viscid droplets strongly appear in the spectrum before spraying water (Fig.…”