Abstract
The β-sheet is the key structure underlying the excellent mechanical properties of spider silk. However, the comprehensive mechanism underlying β-sheet formation from soluble silk proteins during the transition into insoluble stable fibers has not been elucidated. Notably, the assembly of repetitive domains that dominate the length of the protein chains and structural features within the spun fibers has not been clarified. Here we determine the conformation and dynamics of the soluble precursor of the repetitive domain of spider silk using solution-state NMR, far-UV circular dichroism and vibrational circular dichroism. The soluble repetitive domain contains two major populations: ~65% random coil and ~24% polyproline type II helix (PPII helix). The PPII helix conformation in the glycine-rich region is proposed as a soluble prefibrillar region that subsequently undergoes intramolecular interactions. These findings unravel the mechanism underlying the initial step of β-sheet formation, which is an extremely rapid process during spider silk assembly.
Highlights
The β-sheet is the key structure underlying the excellent mechanical properties of spider silk
Several studies have indicated that the C-terminal domains (CTDs) and N-terminal domains (NTDs) are important for maintaining the solubility of spider silk in the major ampullate gland, the size of the CTD and NTD is much smaller than that of the repetitive domain
We investigated the conformations and dynamics of the soluble repetitive domains of N. clavipes in the absence of the terminal domains
Summary
The β-sheet is the key structure underlying the excellent mechanical properties of spider silk. The comprehensive mechanism underlying β-sheet formation from soluble silk proteins during the transition into insoluble stable fibers has not been elucidated. The PPII helix conformation in the glycine-rich region is proposed as a soluble prefibrillar region that subsequently undergoes intramolecular interactions These findings unravel the mechanism underlying the initial step of β-sheet formation, which is an extremely rapid process during spider silk assembly. Spider dragline silks consist of high-molecular-weight proteins (250–350 kDa) that contain conserved and relatively small N-terminal domains (NTDs) and. The conserved NTD and CTD play important roles in spider silk protein self-assembly, the conformational details and role of the long repetitive domain in the soluble form are less well defined and are the focus of the present study for several important reasons. Several studies have indicated that the CTD and NTD are important for maintaining the solubility of spider silk in the major ampullate gland, the size of the CTD and NTD is much smaller than that of the repetitive domain
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