An Engineered Recombinant Spider Silk Protein Providing Disulfide‐Locked Control over Self‐Assembly and Fiber Formation

Abstract Spider silks are renowned for their mechanical properties. The notably tough Argiope trifasciata aciniform silk is spun from a protein predominantly comprising a series of identical 200 residue units (“W units”). In solution, each W unit has a globular 5‐helix domain connected to its neighbors by intrinsically disordered linkers while the fiber contains mixed α‐helical, β‐sheet and disordered structuring. Helix 5 is more dynamic and prone to denaturation than the remainder of the globular domain, implying that it may structurally transform during fiber spinning. Rational cysteine substitutions are introduced at a proximal pair of serines in helix 5 and in helix 1 of the globular domain. Upon disulfide formation, the helix 5 C‐terminal region loses helicity and experiences increased backbone dynamics, while the remainder of the globular structure is effectively unperturbed. Fiber formation by hand‐drawing and wet‐spinning is prevented in the disulfide‐locked state, but readily possible in the reduced (“unlocked”) state. The disulfide‐locked state differs from the unlocked state with much more heterogeneous pre‐fibrillar assembly in spinning dope and through prevention of β‐sheet formation upon cooling following thermal denaturation. This engineered protein thus provides a chemically‐reversible disulfide‐locked state of aciniform silk with modified self‐assembly propensity and fiber formation.