Figure 5. Representative electron micrographs of SOD1 fibrils from spontaneous and seeded reactions (self-seeded and cross-seeded with pre-formed fibril/oligomer or with spinal cord tissue homogenate).

Samples from fibrillization reactions of (A) A4V spontaneous, (B) A4V self-seeded, (C) A4V cross-seeded samples into wtSOD1 protein, (D) G37R spontaneous, (E) G85R spontaneous, (F) G85R self-seeded, (G) G93A spontaneous, (H–I) tgSOD1^G93A spinal cord homogenate seeded into G93A protein. All spontaneous, self- and cross-seeded reactions for all SOD1 variants were carried out at pH4.0 with 0.5M GdnHCl, except for G85R which was carried out at pH5.0 without any denaturant. Shorter fibrillar fragments are indicated by yellow arrows, which were observed in all samples. Green arrows point to longer and continuous fibrillar threads, whereas black arrows indicate thinner and less regular SOD1 species (possibly shorter oligomers). Blue arrows in (E) point to a less structured morphology of G85R ThT-positive species (most appear as spherical aggregates but some have a toroidal appearance) a morphology which was also rarely observed in other SOD1 fibrillar samples. Red arrows in (H) and (I) indicate flexion points of what appears to be 2–3 protofilaments together to form a thicker fibrillar thread or fragment. All SOD1 fibril samples which were qualitatively characterized under EM showed a common property of increased propensity to clump together or to aggregate, regardless of the morphology of the ThT-positive species. Scale bar = 400nm.