Spidroin is produced by a number of arachnids. Spidrions are made up of repetitive segments flanked by conserved non-repetitive domains, and this domain is the conserved non-repetitive region. Aggregation to form the rigid silk occurs due to association at the repetitive regions, and the N-terminal domain is necessary to prevent premature aggregation during storage before extrusion. This N_terminal region inhibits precocious aggregation and then accelerates and directs self-assembly as the pH is lowered along the extrusion duct [1].

1: Self-assembly of spider silk proteins is controlled by a pH-sensitive relay. Askarieh G, Hedhammar M, Nordling K, Saenz A, Casals C, Rising A, Johansson J, Knight SD; Nature. 2010;465:236-238. PMID:20463740