Creating Biomaterials from Plant-derived Recombinant Spider Silk-like Proteins

Biomimetic fibers that resemble the structure and properties of the versatile yet tough spider dragline silk are in high demand. The assembled building blocks of major ampullate dragline silk sequences from Nephila clavipes [Spidroin 1 (Sp1) and Spidroin 2 (Sp2)] are expressed in transgenic Nicotiana tabacum. The plant derived spidroin analogs (mini-spidroins) consist of native Sp1 or Sp 2 N- and C-termini flanking 8, 16, or 32 copies of their respective consensus repeat domains. Gene insertion and RNA transcription were confirmed by PCR and reverse-transcriptase PCR, respectively. Produced mini-spridroins were purified from tobacco using affinity chromatography techniques. After a freeze-drying period, mini-spidroins formed viscous fluids. When purified proteins were treated with acid, cross-linked by glutaraldehyde and diluted in phosphate buffer (pH 7), the mini-spidroins formed a thin film at the layer interface of a counter-ion gellan gum solution. The film was pulled into fibers that displayed auto-fluorescent across a broad range of wavelengths. Fiber mechanical performance was recorded by single displacement controlled tensile test. A method with potential to continuously pull fiber was developed. Fine fibers were produced with more uniform diameter and higher tensile performance.