Genetically Encoded Self-Assembly of Large Amyloid Fibers

“Functional” amyloids are found throughout nature as robust materials. We have discovered that “template” and “adder” proteins cooperatively self-assemble into micrometer-sized amyloid fibers with a controllable, hierarchical structure. Here, Escherichia coli is genetically engineered to express a template protein, Gd20, that can initiate self-assembly of large amyloid fibrils and fibers. Through atomic force microscopy (AFM) we found that expression of Gd20 produces large amyloid fibrils of 490 nm diameter and 2–15 _m length. Addition of an extracellular adder protein, myoglobin, continues self-assembly to form amyloid tapes with widths of [similar]7.5 _m, heights of [similar]400 nm, and lengths exceeding 100 _m. Without myoglobin the amyloid fibrils are metastable over time. When myoglobin is present, the amyloid fiber continues self-assembling to a width of [similar]18 _m and height of [similar]1 _m. Experimental results demonstrate that large amyloid fibers with a tailored stiffness and morphology can be engineered at the DNA level, spanning four orders of magnitude.