Nanoparticle-Templated Formation and Growth Mechanism of Curved Protein Polymer Fibrils

Abstract

We investigated the growth of biosynthetic protein polymers with templated curvature on pluronic nanospheres. The protein has a central silk-like block containing glutamic residues (S(E)) and collagen-like end-blocks (C). The S(E) blocks stack into filaments when their charge is removed (pH <5). Indeed, at low pH curved and circular fibers are formed at the surface of the nanospheres, which keep their shape after removal of the pluronics. The data reveal the mechanism of the templated fibril-growth: The growth of protein assemblies is nucleated in solution; small protein fibrils adsorb on the nanospheres, presumably due to hydrogen bond formation between the silk-like blocks and the pluronic PEO blocks. The surface of the pluronic particles templates further growth. At relatively low protein/pluronic weight ratios, only a fraction of the nanospheres bears protein fibers, pointing to a limiting amount of nuclei in solution. Because the nanospheres capture fibrils at an early stage of growth, they can be used to separate growth and nucleation rates in protein fibril formation. Moreover, the nanoparticle-templated growth of stable curved fibers opens ways to build proteinaceous nanocapsules from designed protein polymers.

Inducible Fibril Formation of Silk–Elastin Diblocks

“…At such critical silk-block lengths n , the amorphous block length m can be used for fine-tuning the assembly behavior. In combination with suitable template-binding blocks, such diblocks allow for nucleic acid encapsulation in silk fibrils, and, for example, may also allow for engineering-induced silk fibril formation on the surfaces of biomaterials, which has also been explored for other silks. − …”