Recombinant DNA techniques were used to prepare a protein modeled after the consensus sequence of Nephila clavipesspider dragline silk, incorporating methionine residues to serve as redox “triggers”. In addition a water-soluble 27 residue peptide model of the dragline silk consensus amorphous sequence, representing a single amorphous block in the protein sequence, was prepared and characterized to gain additional insight into the behavior of the amorphous phase. X-ray diffraction, electron diffraction, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the ability of the recombinant protein to form (β-sheet crystals and the effect of the oxidation state of the redox trigger on crystallinity and noncrystalline order in the sample. The formation of intractable β-sheet crystallites is a major cause of insolubility in proteins that can form this type of secondary structure. Changes in crystallinity were observed when triggered/reduced (insoluble) and untriggered/oxidized (soluble) protein samples were compared.
Quantifying the fraction of glycine and alanine in β-sheet and helical conformations in spider dragline silk using solid-state NMR
