Spidroins are large silk proteins which display relatively conserved terminal domains and a characteristic core repetitive region that amounts to around 90 % of the full length sequence and is believed to dominate the mechanical properties of spider silk. Spidroins are secreted into silk glands and then stably stored where there concentration increases up to 50 % (w/w) allowing them to orderly self-assembled into silk fibers. Spider silks are renowned for their excellent mechanical properties and biomimetic and industrial potentials. The orb-web spiders employ up to seven types of abdominal glands to produce silks for various purposes, ranging from prey capture to offspring protection in egg cases. Egg-case silk fibroins are synthesized only in female tubuliform (cylindrical) silk glands for the construction of protective egg cases, where eggs undergo development. Two spidroins, tubliform spidroin (TuSp1), the major component of egg-case silk, and the recently characterised aciniform spidroin (AcSp1) participate in the egg case formation: AcSp1 forms the inner egg case, while TuSp1 forms the outer egg case. Studies on both proteins have revealed poor sequence similarity between their respective repetitive (RP) domains but a remarkable structural identity, the latter suggests that these two spidroins may share some common characters in fiber formation mechanism and silk fiber properties PMID:23129012,PMID:19458259.