Polarized
Raman spectroscopy is an effective method for analysing features of the protein
structure in spider silk, and most of the early study subjects were
artificially extracted
drag silks of Nephila. To
analyse the relationships between the conformations and properties of different
spider silks in their natural states, polarized Raman spectroscopy was used to
study the web frame silks of
Cyclosa nigra (
C. nigra, belonging
to the genus Cyclosa) and
Achaearanea celsabdomina (
A. celsabdomina,
belonging to the genus Achaearanea), the web frame silk
belongs to the same major ampullate silk as the drag silk. The results show that silks that belong in
a different family have similar amino acid sequences and structures, and
their β-sheets are oriented parallel to the
fibre axis. The difference is that
the most of the other
secondary structures in the
A. celsabdomina silk are oriented perpendicular to the fibre axis; as a result,
A.
celsabdomina silk exhibits a higher ultimate
strain (42.18±11.84%) than
C. nigra silk
(23.85±5.18%). Additionally, the different
ratios of peak intensities and orientation-insensitive spectra indicates that the degree of orientation in the β-sheets
of
A. celsabdomina silk is higher than
that of
C. nigra silk, but the similar contents of β-sheets (the
contents of β-sheets in
C. nigra silk and
A. celsabdomina silk are 32% and 33%, respectively) and hydrogen-bonded Tyr
residues lead to similar breaking strengths for
the two silks (the breaking strengths of
C. nigra silk and
A.
celsabdomina silk are 205.00±25.73 MPa and 236.16±19.46 MPa, respectively). The Raman spectra
of the silks show good consistency, so Raman
spectroscopy can be used to study more varieties
of spider silks, which could offer a theoretical basis for the exploitation and
utilization of spider silks.
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