Spiders' major ampullate silk possesses unique characteristics of strength and elasticity. Fibroin consists of pseudocrystalline regions of antiparallel beta-sheet interspersed with elastic amorphous segments. Major subunit, with spidroin 1, of the dragline silk. Highly repetitive protein characterized by regions of polyalanine and glycine-rich repeating units. Belongs to the silk fibroin family. The tiptoe of an airbus - Issue 24 of July 2002