Pyriform glands secrete fibers that are important constituents of attachment discs. Attachment discs function to fasten dragline silk fibers to solid supports, including wood, concrete, glass, and other surfaces. This attachment is central to locomotion and web construction. The exact mechanism of the adhesion to the support has yet to be fully elucidated. Biochemical studies have revealed that the attachment discs fibers are embedded in a liquid matrix that rapidly dries. The major constituent of attachment disc silks from L. hesperus represents Pyriform Spidroin 1 (PySp1).53 Real-time quantitative PCR analysis support high levels of PySp1 transcripts in the pyriform gland relative to other silk-producing glands. From a protein architecture standpoint, PySp1 contains the conserved C-terminal domain characteristic of spi­droin family members, as well as internal block repeats ranging from 238-300 resi­dues that are rich in A, Q and E, along with a 78 amino acid spacer region that is ex­tremely hydrophilic in nature. Traditional GGX, GPGGX, and poly A stretches are absent. Block modules contain submotifs with the sequence AAARAQAQAEARA — KAE and AAARAQAQAE, which have been shown to form beta-sheet structures

when synthetic peptides containing iterations of these sequences were investigated by circular dichroism (unpublished data). Analysis of the amino acid composition profile reveals the protein sequence of PySp1 contains the most hydrophilic residues relative to other spidroin family members, a likely feature that is linked the observa­tion that it is spun into a liquid matrix that readily dries.53 Because these fibers are difficult to collect from spiders, mechanical data have been difficult to obtain from traditional stress-strain analyzes. In orb-weavers, the equivalent spidroin has been reported and dubbed PySp2 or PiSp1.54 MS/MS analysis ofboth the attachment discs and luminal contents from the pyriform gland of orb-weavers, similar to PySp1, has confirmed the presence of PySp2 as one of the major constituents.54^ Comparable to PySp1, PySp2 contains the highest degree of polarity among the spidroin fam­ily members, conservation within its C-terminal domain, but differences in protein sequence within its internal block repeats relative to the cob-weaver PySp1. PySp2 contains block repeats that are approximately 200 amino acids, flanked by spacer regions that are 44 residues; these spacer regions are Pro-rich and have iterations of the submotif PAPRPXPAPX, with X representing a subset of amino acids that mostly contains hydrophobic R groups. The block motifs have repetitive motifs that are Gln-Gln-Ser-Ser-Val-Ala (QQSSVA). Synthetic fibers spun by wet-spinning methodology with purified proteins containing the C-terminal domain, block repeat, and spacer region have been reported.54a The high degree of polarity within the pro­tein sequences of the PySp fibroins, along with their ability to form fibers, suggests strategies to allow for fabrication of fibers in liquid environments.(Fig. 1.4.)