Multicomponent nature underlies the extraordinary mechanical properties of spider dragline silk

Significance Artificial synthesis of spider silk has been actively pursued. However, until now, the natural mechanical properties of spider silk have been largely unreproducible. We thoroughly investigated the genomes and transcripts of four related species of orb-weaver spiders as well as the proteins in their silk threads. Then, in addition to spidroin, we found several low-molecular-weight proteins in common. Interestingly, the low-molecular-weight protein component of spider dragline silk doubled the tensile strength of artificial silk–based material. This discovery will greatly advance the industry and research on the use of protein-based materials. Dragline silk of golden orb-weaver spiders (Nephilinae) is noted for its unsurpassed toughness, combining extraordinary extensibility and tensile strength, suggesting industrial application as a sustainable biopolymer material. To pinpoint the molecular composition of dragline silk and the roles of its constituents in achieving its mechanical properties, we report a multiomics approach, combining high-quality genome sequencing and assembly, silk gland transcriptomics, and dragline silk proteomics of four Nephilinae spiders. We observed the consistent presence of the MaSp3B spidroin unique to this subfamily as well as several nonspidroin SpiCE proteins. Artificial synthesis and the combination of these components in vitro showed that the multicomponent nature of dragline silk, including MaSp3B and SpiCE, along with MaSp1 and MaSp2, is essential to realize the mechanical properties of spider dragline silk.