Structural Model for the Spider Silk Protein Spidroin‑1

Most reports about the 3-D structure
of spidroin-1 have been proposed
for the protein in solid state or for individual domains of these
proteins. A gel-based mass spectrometry strategy using collision-induced
dissociation (CID) and electron-transfer dissociation (ETD) fragmentation
methods was used to completely sequence spidroins-1A and -1B and to
assign a series of post-translational modifications (PTMs) on to the
spidroin sequences. A total of 15 and 16 phosphorylation sites were
detected on spidroin-1A and -1B, respectively. In this work, we present
the nearly complete amino acid sequence of spidroin-1A and -1B, including
the nonrepetitive N- and C-terminal domains and a highly repetitive
central core. We also described a fatty acid layer surrounding the
protein fibers and PTMs in the sequences of spidroin-1A and -1B, including
phosphorylation. Thus, molecular models for phosphorylated spidroins
were proposed in the presence of a mixture fatty acids/water (1:1)
and submitted to molecular dynamics simulation. The resulting models
presented high content of coils, a higher percentage of α-helix,
and an almost neglected content of 310-helix than the previous
models. Knowledge of the complete structure of spidroins-1A and -1B
would help to explain the mechanical features of silk fibers. The
results of the current investigation provide a foundation for biophysical
studies of the mechanoelastic properties of web-silk proteins.