The molecular structure of novel pyriform spidroin (PySp2) reveals extremely complex central repetitive region

Orb-weaving spiders produce a diversity of silk fibers throughout their entire lifecycle, and each silk type is given a specific purpose. As a dry fiber material with wet glue, pyriform silks are different from other silk fibers and make the attachment discs which are used for bonding fibers together and attaching dragline silk to other substrates. To date, only two full-length pyriform spidroin 1 (PySp1) gene sequences were identified. Here we present a novel full-length pyriform spidroin 2 (PySp2) from orb-weaving spider, Araneus ventricosus. Although the A. ventricosus PySp2 lack the long linker regions, the central repetitive region of PySp2 is more complex than PySp1 and can be classified into four types of repetitive regions including three novel repetitive sequences and one type of repetitive region that is similar to PySp1 repeats. Prediction of hydrophobicity of A. ventricosus PySp2 reveals the two new repetitive regions display strong hydrophilicity. Analysis of CD spectrum and secondary structure prediction for A. ventricosus PySp2 repeat unit reveal α-helix conformation dominates the repetitive region. Furthermore, recombinant protein-based artificial fibers show the single repeat unit is sufficient for self-assembling into silk fiber.