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'''5IZ2''' is the '''N-terminal domain (NTD)''' of a spider protein called '''Major ampullate Spidroin 1A (MaSp1A)''', coming from the ''Nephila Clavipes'' species. This protein is a component of dragline silk produced in the major ampullate gland of spiders<ref name="Atkison"/>. The NTD domain of MaSp1A plays a major role in their combination during silk production <ref name="Atkison"/>. Indeed, thanks to the NTD dimerisation, two MaSps can be connected, leading to the formation of '''fibers''' with exceptional physical and biochemical qualities <ref name="José">José Roberto Aparecido dos Santos-Pinto, Helen Andrade Arcuri, Helga Priewalder, Heliana Clara Salles, Mario Sergio Palma and Gert Lubec, 2015. Structural Model for the Spider Silk Protein Spidroin‑1, Journal of Proteome research, 14, p.3859-3870.</ref>. It is of biotechnological interest to deeply understand the NTD dimerisation mechanism for the production of artificial spider silk, which can lead to innovative biomaterials.

The study of the ''N. Clavipes'' NTD permits to compare its structure with other species thus to provide new insights into the mechanism of NTD dimerization. Moreover, silks produced from different spider breeds vary in physical properties such as toughness and elasticity. In this way, studying diverse species would allow to '''optimize artificial silk''' for different applications.

==Generalities on fiber assembly of dragline silks==

The process of the dragline fiber formation is the connection of '''soluble MaSp''' proteins into '''insoluble fibers'''. Indeed, MaSps are firstly secreted and stored in soluble form in the tail of the major ampullate gland which is located in the spider’s abdomen. On demand, they pass through the narrow duct where they experience mechanical and chemical forces that convert them into fibers. Actually, they deal with a pH dropping, an alteration of ion concentrations and oxidation conditions, which occur gradually along the duct. These changes promote the connection of MaSps extremities (i.e. homo-dimerisation of C- and N-terminal domains) to form fibers. Finally, through flow rate and mechanical forces experienced in the duct, the fibers will agglomerate to create the '''dragline silk'''.

==Overall structure of Major Ampullate Spidroin==

*'''N-terminal domain (NTD)''':  

This domain is the most highly conserved domain. NTD dimerises in the duct upon conditions change, which connects the MaSps to form fibers.

== Monomer structure of the spidroin NTD domain ==