Biophysical Society Thematic Meeting - October 25-30, 2015

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Polymers and Self Assembly: From Biology to Nanomaterials Tuesday Speaker Abstracts
Spider Silk Assembly is Mediated by a Lock and Trigger Mechanism
Anna Rising
Karolinska Institutet, Sweden
No abstract
Development of Recombinant Spider Silk Proteins with Tunable Assembly Properties for
Biomimetic Spinning
Jan Johansson 1,2, Anna Rising1,2.
1Karolinska Institutet, Huddinge, Sweden, 2SLU, Ultuna, Sweden.
Spiders use specialized glands to make different types of protein-based silks with remarkable
biochemical and mechanical properties, and artificial spider silk could be an ideal source for
generation of novel high performance biomaterials. Spider silk fibres contain crystalline β-sheet
regions, which mediate mechanical stability and that are formed within fractions of a second in
the end of the spinning duct, but the soluble silk proteins (spidroins) can be stored at huge
concentrations in the silk gland for long times, without aggregating prematurely. These
properties have so far not been mimicked by recombinant spidroins. Spidroins contain unique
repetitive segments, which determine the mechanical properties of the silk, as well as non-
repetitive N- and C-terminal domains (NT and CT), which regulate conversion of the dope into
fibres. We have studied the physiological regulation of spider silk formation and the molecular
actions of NT and CT in detail. NT employs an evolutionarily conserved pH dependent three-
step mechanism to decouple dimerization from locking of the dimer structure – a mechanism that
ensures both rapid β-sheet aggregation and prevention of premature silk assembly. CT, in
contrast, gets destabilised and converts into amyloid-like fibrils in a pH and CO2 dependent
manner, a hitherto unique mechanism that we suggest is important for nucleating the formation
of β-sheets in the silk fibres.
We now use this knowledge to develop novel miniature spidroins with optimal properties in
terms of solubility, yields upon recombinant production, and stability. A first generation of
novel, designed minispidroins that show very high expression yields and solubility, and that can
convert into fibres using a biomimetic spinning procedure have been generated. These
minispidroins also allow high-resolution studies of spidroin structures in soluble and fibrillar
states.