Solid state NMR investigations of protein based biomaterials: spider silk, recombinant spider silk proteins, and electrospun spider silk proteins

¹³C Nuclear Magnetic Resonance was employed to investigate the structure of spider dragline silk, powdered recombinant major ampulate spidroin 1 (MaSp1) and 2 (MaSp2) that were produced in the milk of genetically engineered goats, and electrospun MaSp1. Cross polarization spectra were used to assign secondary structures to the protein residues, and longitudinal relaxation measurements were used to investigate the molecular thermal motion. The crystalline regions of spider silk were found to exhibit nanosecond scale thermal motion, subject to very rigid motional limits. The recombinant MaSp1 and MaSp2 were found to have very similar structures that exhibited abundant β sheet crystalline regions. Electrospun MaSp1 however appears to be highly disordered and is perhaps best characterized as denatured. These results are in contrast to previous findings of spider silk proteins in non-fiber states, where no appreciable crystalline component was observed, and appears to be inconsistent with previous Fourier transform infrared spectroscopy of similarly prepared samples. Reconsideration of the FTIR data however raises concerns about the interpretation of those data, possibly explaining the disagreement. This work suggests that the lack of regular structure found in the electrospun MaSp1 is the cause of the very poor mechanical properties previously measured for this material.