Abstract

Compared to other arthropods, spiders are unique in their use of silks throughout their life span and the extraordinary mechanical properties of their silks. So far, studies on spider silk proteins have been focused on orb-web-weaving spiders, little is known on non-orb weavers' silk proteins. To expand our knowledge on these spider silk proteins, a cDNA library was constructed and screened from Agelenopsis aperta major ampullate gland. Sequencing of major ampullate silk cDNAs reveals the repetitive architecture of the coding sequence. The inferred protein, A. aperta Major contains highly homogenized repeat units which share over 81% sequence similarity at both DNA and amino acid level. Amino acid composition comparison of A. aperta Major sequence to the major ampullate gland protein indicates that A. aperta Major is the major component of the gland. Codon usage analysis of A. aperta Major coding sequence shows strongly biased codon preference to adenine and thymine at the wobble position.

Tubuliform (eggcase) silk is a unique silk among the seven silks produced by orb-web-weaving spiders. To understand the molecular characteristics of the proteins composing this silk, I constructed tubuliform gland specific cDNA libraries from three spiders, Nephila clavipes, Argiope aurantia and Araneus gemmoides, respectively. Sequencing of tubuliform silk cDNAs reveals the repetitive structure of the coding sequence and novel amino acid motifs. The inferred protein, tubuliform spidroin 1 (TuSp1) contains highly homogenized repeats in all three spiders. Amino acid composition comparison of TuSp1 protein sequence to tubuliform gland protein indicates that TuSp1 is the major component of tubuliform silk. Repeat unit alignment of TuSp1 among three spiders exhibits high conservation within TuSp1 orthologue groups. Sequence comparison among TuSp1 repetitive units within species suggests intragenic concerted evolution, presumably, through gene conversion and unequal cross over events. Comparative analysis demonstrates that TuSp1 represents a new orthologue in spider silk fibroin family.