Figure 4.
Morphology of fatty-acid-(OV)4 precipitates compared to pure (OV)4 amyloids. Cryo-EM micrographs of the flocculent precipitate (A) and translucent precipitate (B) formed in mixtures of DA and (OV)4. The flocculent precipitate is usually too thick for observing detailed morphological features, but in a few instances like the one depicted in (A), fibrillar structures are visible. The translucent precipitate is characterized by straight fiber-like structures that have a uniform width of ∼25 nm and lengths of up to several microns. In many of the tube-like structures, there is a visible striation, indicating that they may be composed of an alignment of smaller fibrils (C). The translucent precipitates of (OV)4 mixtures with NA (D) and DDA (E) also reveal fiber-like structures; however, they present a distribution of widths. The NA samples have a narrow distribution, whereas the DDA/(OV)4 mixtures have structures with a much larger variation in width. The amyloid fibrils of (OV)4 that form at pH 11 (F) are characterized by many straight fibers that form bundles of varying numbers of protofilaments.