Chemical Synthesis of Multiblock Copolypeptides Inspired by Spider Dragline Silk Proteins

Novel multiblock polypeptides with a structure similar to the unique sequence observed in spider silk proteins (spidroins) were synthesized via a two-step chemical synthesis method, that is, chemoenzymatic polymerization, using papain followed by postpolycondensation. Two types of polypeptide fragments were prepared by chemoenzymatic polymerization: polyalanine as a hard block, which forms ?-sheets in the spider silk fibers, and poly(glycine-random-leucine) as a soft block. These two fragments were ligated by postpolycondensation using polyphosphoric acid as a condensing agent. Wide-angle X-ray diffraction (WAXD) and IR measurements revealed that the resulting multiblock polypeptides formed an antiparallel ?-sheet structure with a degree of crystallinity similar to that of spider silk, which resulted in a fibrous morphology. This work provides the first example of a synthetic multiblock polypeptide mimicking the secondary structures of spider silk.