In the silk glands of the spiders, the silk precursors is contained in liquid form and became solid when it is excreted. The dimerization of the N-terminal domain of MaSp1 involved the transition from the liquid form to the solid silk.
Function
MaSp1 is one of the proteins which composed the spider silk. The N-terminal domain (NT) is important to change from the soluble conformation of MaSp1 to the insoluble of this protein. In the soluble conformation the most important secondary structure is α-helix, in the insoluble conformation the protein is mostly composed of β-sheets. Dimerization of NT create fiber of spider silk and the changing conformation from α-helix to β-sheets make the spider silk insoluble. The dimerization of NT is induced by the lowering of pH from 7 to 6.
Relevance
Understand the polymerization of spider silks is important to produce this in vitro and in great quantity. Indeed the militaty and biomedical fields need spider silks to develop different product like bullet proof vest, artifical bones and artifical ligament.
Structural highlights
For the monomeric NT helix 2 and helix 3 forme a subunit and helix 1,4 and 5 forme a second subunit. There is a rotation of 16° between the subunits to create an open five-helix. In the dimeric NT helix 2,3 and 5 create a subunits, this changing of conformation is mostly induced by the burial of . So this amino acid go from hydophobic environment to hydrophilic environment. This conformation is stablized by the interaction of (the beginning of helix 2) and glutamic acid 84 (at the end of helix 3). This interaction is impossible in monomeric NT because the two amino acids are separate by more of 10 Å. Also the protonation of is most important event to pass from the monomeric form to the dimeric form between pH 6 and 7. But if the pH lowering too much (below pH 4) will be protonated and this destablize the dimer.
is very conserverved in most of the species but it can be repleased by phenylalanin.
