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 coliis 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 mu m length. Addition of an extracellular adder protein, myoglobin, continues self-assembly to form amyloid tapes with widths of similar to 7.5 mu m, heights of similar to 400 nm, and lengths exceeding 100 mu 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 to 18 mu m and height of similar to 1 mu 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.