Abstract
The extraordinary mechanical properties of spider dragline silk are dependent on the highly repetitive sequences of the component proteins, major ampullate spidroin 1 and 2 (MaSp2 and MaSp2). MaSp sequences are dominated by repetitive modules composed of short amino acid motifs; however, the patterns of motif conservation through evolution and their relevance to silk characteristics are not well understood. We performed a systematic analysis of MaSp sequences encompassing infraorder Araneomorphae based on the conservation of explicitly defined motifs, with the aim of elucidating the essential elements of MaSp1 and MaSp2. The results show that the GGY motif is nearly ubiquitous in the two types of MaSp, while MaSp2 is invariably associated with GP and di-glutamine (QQ) motifs. Further analysis revealed an extended MaSp2 consensus sequence in family Araneidae, with implications for the classification of the archetypal spidroins ADF3 and ADF4. Additionally, the analysis of RNA-seq data showed the expression of a set of distinct MaSp-like variants in genus Tetragnatha. Finally, an apparent association was uncovered between web architecture and the abundance of GP, QQ, and GGY motifs in MaSp2, which suggests a co-expansion of these motifs in response to the evolution of spiders' prey capture strategy.
Highlights
Spiders produce multiple types of silk to fulfill a variety of biological tasks, including web construction, prey wrapping, and protection of eggs [1]
The deduced consensus motif criteria were cross-validated against the collection of Major ampullate spidroin (MaSp) and MaSp-like sequences found in GenBank encompassing infraorder Araneomorphae, including sequences from cDNA libraries originating from major ampullate silk glands, as well as sequences derived from genomic DNA that have previously been classified as MaSp1 or MaSp2
Only long sequences originating from major ampullate gland cDNA libraries were included in the primary analysis; the shortest sequence used, ADF4 from A. diadematus, contained 302 residues in the reported repetitive sequence, and contained eight complete tandem repeats
Summary
Spiders produce multiple types of silk to fulfill a variety of biological tasks, including web construction, prey wrapping, and protection of eggs [1]. Spiders use dragline silk as a safety line and as a major component of webs, and constitutes the frame and main radii of orb-type webs. The extreme strength and toughness of dragline silk are critical for the absorption and dissipation of the kinetic energy imparted by swiftly flying insects on the web structures [2, 3]. Spider silks are composed primarily of spidroins, structural proteins whose architecture usually consists of a long, repetitive central domain flanked by conserved globular amino- and carboxyl-terminal domains (NTD and CTD) [4]. The different spider silks are associated with
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