fl-Sheet Structure Formation within Binary Blends of Two Spider Silk Related Peptides

Intrinsically disordered proteins (IDPs) play an important role in molecular biology and medicine because their induced folding can lead to so-called conformational diseases, where fi-amyloids play an important role. Still, the molecular folding process into the different substructures, such as parallel/ antiparallel or extended fi-sheet/crossed fi-sheet is not fully understood. The recombinant spider silk protein eADF4(Cx) consisting of repeating modules C, which are composed of a crystalline (pep-c) and an amorphous peptide sequence (pep-a), can be used as a model system for IDP since it can assemble into similar structures. In this work, blend films of the pep-c and pep-a sequences were investigated to modulate the fi-sheet formation by varying the molar fraction of pep-c and pep-a. Dichroic Fourier transform infrared spectroscopy (FTIR), circular dichroism, spectroscopic ellipsometry, atomic force microscopy, and IR nanospectroscopy were used to examine the secondary structure, the formation of parallel and antiparallel fi-sheets, their orientation, and the microscopic roughness and phase formation within peptide blend films upon methanol post-treatment. New insights into the formation of filament-like structures in these silk blend films were obtained. Filament-like structures could be locally assigned to fi- sheet-rich structures. Further, the antiparallel or parallel character and the orientation of the formed fi-sheets could be clearly determined. Finally, the ideal ratio of pep-a and pep-c sequences found in the fibroin 4 of the major ampullate silk of spiders could also be rationalized by comparing the blend and spider silk protein systems.

Automated summary

By studying blend films of silk proteins, researchers investigated the molecular folding process and revealed the formation and orientation of filament-like structures in these films. They also compared the similarities between silk proteins and spider silk proteins.