Twisted transthyretin

Figure 14.8 Proposed model of p sheet helix of the fibrous form of transthyretin. The repeating unit of the P helix comprises 24 P strands with an average twist of 15° between each strand giving a complete turn of 360°. Four transthyretin polypeptide chains contribute to the repeat unit and are shown here in different colors. (Adapted from C. Blake and L. Serpell, Structure 4 989-998, 1996.)...

Fig. 2. Electron micrographs highlighting the polymorphism of amyloid fibrils. (A) A single human calcitonin protofibril with a diameter of 4 nm (adapted from Bauer et al., 1995). (B) Different morphologies present in a transthyretin fibril preparation. Black arrowheads show oligomers of different sizes, the black arrow points to a 9- to 10-nm-wide fibril, and the white arrowhead marks an 4-nm-wide fibril (adapted from Cardoso et al., 2002). (C-F) Human amylin fibril ribbons (adapted from Goldsbury et al., 1997). (C) A single 5-nm-wide protofibril. (D-F) Ribbons containing two (D), three (E), or five (F) 5-nm-wide protofibrils. (G) A twisted ribbon made of four 5-nm-wide protofibril subunits of Api-40 (adapted from Goldsbury et al., 2000b). Scale bar, 50 nm (A-G).

Parallel fl-Sheet Proteins. The most common arrangement in this class contains four strands for each sheet to form the natural twist such as prealbumin. However, the directions of the strands are not all equivalent and the connectivities of the strands are different, such as transthyretin (Figure 12.1c). 

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