Analysis of Aqueous Glue Coating Proteins on the Silk Fibers of the Cob Weaver, Latrodectus hesperus

Abstract

Elucidation of the molecular composition and physical properties of spider glue is necessary to understand its function in the mechanics of the web and prey capture. Previous reports have indicated that components of the adhesive coating contain inorganic molecules, phosphorylated glycoproteins, lipids, and organic low-molecular mass (LMM) compounds. Using a proteomic strategy, we have investigated the viscid, aqueous components that coat different silk fiber types from the black widow spider, Latrodectus hesperus. After in-solution tryptic digestion of the aqueous protein material extracted from egg case sacs, gumfooted lines, and the web scaffolding connection joints, followed by peptide analysis using MALDI tandem TOF mass spectrometry, we demonstrate that these fibers are coated with common peptides. Utilizing a reverse genetics approach, we have isolated the cDNAs encoding two distinct fiber coating products, which we have named spider coating peptide 1 and 2 (SCP-1 and SCP-2). Secreted forms of SCP-1 and SCP-2 contain 36 and 19 amino acids, respectively, and their primary sequences display no significant similarities to ensemble repeat units from traditional fibroins. Quantitative real-time reverse transcription PCR analyses show that these mRNAs are chiefly produced by the aggregate gland. Biochemical studies also demonstrate that the SCP-1 peptide has intrinsic metal binding properties, suggesting a role of peptide-metal ion interactions with the fiber constituents to enhance thread performance. Collectively, these investigations are the first to reveal a novel role for the aggregate gland in the production of peptides that coat spider silk threads.

The elaborate structure of spider silk

“…To retain prey in the web, additional glue is applied around the capture threads. 8 Evolutionarily, the first adhesive was a special silk fiber which was hackled by comblike devices, cribella, on the spider's hind legs in order to achieve a maximum surface area. The adhesive properties of cribellate silk are mainly based on a large sum of van-der-Waals forces provided by huge surface areas similar to the adhesion principle of gecko feet, where an extremely large surface area is provided by nano hairs on the toes.…”

“…11,12 Recently, it was proposed that the wet glue also contains small peptides which are thought to function as metal chelators. 8 The presence of metal ions might contribute to the inhibition of microbial growth on silk threads which is crucial to protecting the web or preventing damage to developing eggs. Wet glue is more energy-and time-efficient (compared to the cribellate system) and is therefore used by the majority of today's spiders.…”

The role of terminal domains during storage and assembly of spider silk proteins

“…31 Under such storage conditions, micellar-like structures of the spidroins have been reported, likely presenting a metastable state to prevent undesirable aggregation. [32][33][34] The assembly process is initiated in the tapered S-shaped spinning duct where sodium and chloride ions are exchanged for the more kosmotropic potassium and phosphate ions, accompanied by a reduction of the pH value to about 6.2. As shear forces increase along the duct, b-sheet…”

Parasitoid suppression and life-history modifications in a wolf spider following infection by larvae of an acrocerid fly

“…Most spider silk proteins are encoded by members of the spidroin gene family, whose evolutionary history is characterized by bouts of gene duplication followed by strong diversification (Gatesy et al 2001;Gaines & Marcotte 2008;Garb et al 2010). However, some recently discovered silk proteins are difficult to homologize to the known spider silk gene family -in particular some of the proteins found in the piriform attachments that cement threads together (Hu et al 2007).…”

“…For instance, the sticky gumfooted threads in the cobwebs of theridiid spiders act as spring-loaded traps where energy is stored within the structure of the cobweb during prey capture (Argintean et al 2006), rather than dissipated as in orb webs. The glue coating the gumfoot threads also differs in microstructure and adhesive response to humidity (Sahni et al 2011b), as well as containing unique proteins (Hu et al 2007). Unfortunately, nothing is known about the diversity of mechanical properties among the silk of different species of cobweb spiders, let alone anything about functional differences in their webs.…”