Structural Model for the Spider Silk Protein Spidroin-1.

Area of Science:

• Biochemistry
• Materials Science
• Structural Biology

Background:

• Previous studies focused on solid-state or domain-specific structures of spidroin-1.
• A comprehensive understanding of spidroin-1's complete structure, including modifications, is lacking.

Purpose of the Study:

• To determine the complete amino acid sequence of spidroins-1A and -1B.
• To identify post-translational modifications (PTMs) and characterize the structural impact of phosphorylation and fatty acid interactions.
• To generate molecular models and simulate the behavior of phosphorylated spidroins.

Main Methods:

• Gel-based mass spectrometry utilizing collision-induced dissociation (CID) and electron-transfer dissociation (ETD) for protein sequencing.
• Identification and localization of post-translational modifications, specifically phosphorylation sites.
• Molecular dynamics simulations of proposed models for phosphorylated spidroins in a fatty acid/water mixture.

Main Results:

• Nearly complete amino acid sequences for spidroins-1A and -1B were obtained, including terminal and core domains.
• 15 and 16 phosphorylation sites were identified on spidroin-1A and -1B, respectively, along with a surrounding fatty acid layer.
• Molecular dynamics simulations revealed models with increased coil and alpha-helix content and reduced 310-helix content compared to prior models.

Conclusions:

• The study provides a comprehensive sequence and structural characterization of spidroins-1A and -1B, including PTMs.
• The findings offer insights into the structural basis of spider silk's mechanical properties.
• This work lays the groundwork for future biophysical investigations into the mechanoelastic properties of web-silk proteins.